diff --git a/legacy/firmware/Makefile b/legacy/firmware/Makefile
index cbe61fe69..b5ad3f030 100644
--- a/legacy/firmware/Makefile
+++ b/legacy/firmware/Makefile
@@ -96,7 +96,8 @@ OBJS += ../vendor/trezor-storage/norcow.o
 
 OBJS += ../vendor/nanopb/pb_common.o
 OBJS += ../vendor/nanopb/pb_decode.o
-OBJS += ../vendor/nanopb/pb_encode.o
+# we have a local patch in pb_encode.c
+OBJS += pb_encode.o
 
 OBJS += protob/messages.pb.o
 OBJS += protob/messages-bitcoin.pb.o
diff --git a/legacy/firmware/pb_encode.c b/legacy/firmware/pb_encode.c
new file mode 100644
index 000000000..c9b54fe6f
--- /dev/null
+++ b/legacy/firmware/pb_encode.c
@@ -0,0 +1,874 @@
+// clang-format off
+
+/* pb_encode.c -- encode a protobuf using minimal resources
+ *
+ * 2011 Petteri Aimonen <jpa@kapsi.fi>
+ */
+
+#include "pb.h"
+#include "pb_encode.h"
+#include "pb_common.h"
+
+/* Use the GCC warn_unused_result attribute to check that all return values
+ * are propagated correctly. On other compilers and gcc before 3.4.0 just
+ * ignore the annotation.
+ */
+#if !defined(__GNUC__) || ( __GNUC__ < 3) || (__GNUC__ == 3 && __GNUC_MINOR__ < 4)
+    #define checkreturn
+#else
+    #define checkreturn __attribute__((warn_unused_result))
+#endif
+
+/**************************************
+ * Declarations internal to this file *
+ **************************************/
+typedef bool (*pb_encoder_t)(pb_ostream_t *stream, const pb_field_t *field, const void *src) checkreturn;
+
+static bool checkreturn buf_write(pb_ostream_t *stream, const pb_byte_t *buf, size_t count);
+static bool checkreturn encode_array(pb_ostream_t *stream, const pb_field_t *field, const void *pData, size_t count, pb_encoder_t func);
+static bool checkreturn encode_field(pb_ostream_t *stream, const pb_field_t *field, const void *pData);
+static bool checkreturn default_extension_encoder(pb_ostream_t *stream, const pb_extension_t *extension);
+static bool checkreturn encode_extension_field(pb_ostream_t *stream, const pb_field_t *field, const void *pData);
+static void *pb_const_cast(const void *p);
+static bool checkreturn pb_enc_varint(pb_ostream_t *stream, const pb_field_t *field, const void *src);
+static bool checkreturn pb_enc_uvarint(pb_ostream_t *stream, const pb_field_t *field, const void *src);
+static bool checkreturn pb_enc_svarint(pb_ostream_t *stream, const pb_field_t *field, const void *src);
+static bool checkreturn pb_enc_fixed32(pb_ostream_t *stream, const pb_field_t *field, const void *src);
+static bool checkreturn pb_enc_fixed64(pb_ostream_t *stream, const pb_field_t *field, const void *src);
+static bool checkreturn pb_enc_bytes(pb_ostream_t *stream, const pb_field_t *field, const void *src);
+static bool checkreturn pb_enc_string(pb_ostream_t *stream, const pb_field_t *field, const void *src);
+static bool checkreturn pb_enc_submessage(pb_ostream_t *stream, const pb_field_t *field, const void *src);
+static bool checkreturn pb_enc_fixed_length_bytes(pb_ostream_t *stream, const pb_field_t *field, const void *src);
+
+#ifdef PB_WITHOUT_64BIT
+#define pb_int64_t int32_t
+#define pb_uint64_t uint32_t
+
+static bool checkreturn pb_encode_negative_varint(pb_ostream_t *stream, pb_uint64_t value);
+#else
+#define pb_int64_t int64_t
+#define pb_uint64_t uint64_t
+#endif
+
+/* --- Function pointers to field encoders ---
+ * Order in the array must match pb_action_t LTYPE numbering.
+ */
+static const pb_encoder_t PB_ENCODERS[PB_LTYPES_COUNT] = {
+    &pb_enc_varint,
+    &pb_enc_uvarint,
+    &pb_enc_svarint,
+    &pb_enc_fixed32,
+    &pb_enc_fixed64,
+    
+    &pb_enc_bytes,
+    &pb_enc_string,
+    &pb_enc_submessage,
+    NULL, /* extensions */
+    &pb_enc_fixed_length_bytes
+};
+
+/*******************************
+ * pb_ostream_t implementation *
+ *******************************/
+
+static bool checkreturn buf_write(pb_ostream_t *stream, const pb_byte_t *buf, size_t count)
+{
+    size_t i;
+    pb_byte_t *dest = (pb_byte_t*)stream->state;
+    stream->state = dest + count;
+    
+    for (i = 0; i < count; i++)
+        dest[i] = buf[i];
+    
+    return true;
+}
+
+pb_ostream_t pb_ostream_from_buffer(pb_byte_t *buf, size_t bufsize)
+{
+    pb_ostream_t stream;
+#ifdef PB_BUFFER_ONLY
+    stream.callback = (void*)1; /* Just a marker value */
+#else
+    stream.callback = &buf_write;
+#endif
+    stream.state = buf;
+    stream.max_size = bufsize;
+    stream.bytes_written = 0;
+#ifndef PB_NO_ERRMSG
+    stream.errmsg = NULL;
+#endif
+    return stream;
+}
+
+bool checkreturn pb_write(pb_ostream_t *stream, const pb_byte_t *buf, size_t count)
+{
+    if (stream->callback != NULL)
+    {
+        if (stream->bytes_written + count > stream->max_size)
+            PB_RETURN_ERROR(stream, "stream full");
+
+#ifdef PB_BUFFER_ONLY
+        if (!buf_write(stream, buf, count))
+            PB_RETURN_ERROR(stream, "io error");
+#else        
+        if (!stream->callback(stream, buf, count))
+            PB_RETURN_ERROR(stream, "io error");
+#endif
+    }
+    
+    stream->bytes_written += count;
+    return true;
+}
+
+/*************************
+ * Encode a single field *
+ *************************/
+
+/* Encode a static array. Handles the size calculations and possible packing. */
+static bool checkreturn encode_array(pb_ostream_t *stream, const pb_field_t *field,
+                         const void *pData, size_t count, pb_encoder_t func)
+{
+    size_t i;
+    const void *p;
+    size_t size;
+    
+    if (count == 0)
+        return true;
+
+    if (PB_ATYPE(field->type) != PB_ATYPE_POINTER && count > field->array_size)
+        PB_RETURN_ERROR(stream, "array max size exceeded");
+    
+    /* We don't pack arrays even if the datatype allows it. */
+    if (0)
+    {
+        if (!pb_encode_tag(stream, PB_WT_STRING, field->tag))
+            return false;
+        
+        /* Determine the total size of packed array. */
+        if (PB_LTYPE(field->type) == PB_LTYPE_FIXED32)
+        {
+            size = 4 * count;
+        }
+        else if (PB_LTYPE(field->type) == PB_LTYPE_FIXED64)
+        {
+            size = 8 * count;
+        }
+        else
+        { 
+            pb_ostream_t sizestream = PB_OSTREAM_SIZING;
+            p = pData;
+            for (i = 0; i < count; i++)
+            {
+                if (!func(&sizestream, field, p))
+                    return false;
+                p = (const char*)p + field->data_size;
+            }
+            size = sizestream.bytes_written;
+        }
+        
+        if (!pb_encode_varint(stream, (pb_uint64_t)size))
+            return false;
+        
+        if (stream->callback == NULL)
+            return pb_write(stream, NULL, size); /* Just sizing.. */
+        
+        /* Write the data */
+        p = pData;
+        for (i = 0; i < count; i++)
+        {
+            if (!func(stream, field, p))
+                return false;
+            p = (const char*)p + field->data_size;
+        }
+    }
+    else
+    {
+        p = pData;
+        for (i = 0; i < count; i++)
+        {
+            if (!pb_encode_tag_for_field(stream, field))
+                return false;
+
+            /* Normally the data is stored directly in the array entries, but
+             * for pointer-type string and bytes fields, the array entries are
+             * actually pointers themselves also. So we have to dereference once
+             * more to get to the actual data. */
+            if (PB_ATYPE(field->type) == PB_ATYPE_POINTER &&
+                (PB_LTYPE(field->type) == PB_LTYPE_STRING ||
+                 PB_LTYPE(field->type) == PB_LTYPE_BYTES))
+            {
+                if (!func(stream, field, *(const void* const*)p))
+                    return false;
+            }
+            else
+            {
+                if (!func(stream, field, p))
+                    return false;
+            }
+            p = (const char*)p + field->data_size;
+        }
+    }
+    
+    return true;
+}
+
+/* In proto3, all fields are optional and are only encoded if their value is "non-zero".
+ * This function implements the check for the zero value. */
+static bool pb_check_proto3_default_value(const pb_field_t *field, const void *pData)
+{
+    pb_type_t type = field->type;
+    const void *pSize = (const char*)pData + field->size_offset;
+
+    if (PB_HTYPE(type) == PB_HTYPE_REQUIRED)
+    {
+        /* Required proto2 fields inside proto3 submessage, pretty rare case */
+        return false;
+    }
+    else if (PB_HTYPE(type) == PB_HTYPE_REPEATED)
+    {
+        /* Repeated fields inside proto3 submessage: present if count != 0 */
+        if (field->size_offset != 0)
+            return *(const pb_size_t*)pSize == 0;
+        else
+            return false; /* Fixed length array */
+    }
+    else if (PB_HTYPE(type) == PB_HTYPE_ONEOF)
+    {
+        /* Oneof fields */
+        return *(const pb_size_t*)pSize == 0;
+    }
+    else if (PB_HTYPE(type) == PB_HTYPE_OPTIONAL && field->size_offset != 0)
+    {
+        /* Proto2 optional fields inside proto3 submessage */
+        return *(const bool*)pSize == false;
+    }
+
+    /* Rest is proto3 singular fields */
+
+    if (PB_ATYPE(type) == PB_ATYPE_STATIC)
+    {
+        if (PB_LTYPE(type) == PB_LTYPE_BYTES)
+        {
+            const pb_bytes_array_t *bytes = (const pb_bytes_array_t*)pData;
+            return bytes->size == 0;
+        }
+        else if (PB_LTYPE(type) == PB_LTYPE_STRING)
+        {
+            return *(const char*)pData == '\0';
+        }
+        else if (PB_LTYPE(type) == PB_LTYPE_FIXED_LENGTH_BYTES)
+        {
+            /* Fixed length bytes is only empty if its length is fixed
+             * as 0. Which would be pretty strange, but we can check
+             * it anyway. */
+            return field->data_size == 0;
+        }
+        else if (PB_LTYPE(type) == PB_LTYPE_SUBMESSAGE)
+        {
+            /* Check all fields in the submessage to find if any of them
+             * are non-zero. The comparison cannot be done byte-per-byte
+             * because the C struct may contain padding bytes that must
+             * be skipped.
+             */
+            pb_field_iter_t iter;
+            if (pb_field_iter_begin(&iter, (const pb_field_t*)field->ptr, pb_const_cast(pData)))
+            {
+                do
+                {
+                    if (!pb_check_proto3_default_value(iter.pos, iter.pData))
+                    {
+                        return false;
+                    }
+                } while (pb_field_iter_next(&iter));
+            }
+            return true;
+        }
+    }
+    
+	{
+	    /* Catch-all branch that does byte-per-byte comparison for zero value.
+	     *
+	     * This is for all pointer fields, and for static PB_LTYPE_VARINT,
+	     * UVARINT, SVARINT, FIXED32, FIXED64, EXTENSION fields, and also
+	     * callback fields. These all have integer or pointer value which
+	     * can be compared with 0.
+	     */
+	    pb_size_t i;
+	    const char *p = (const char*)pData;
+	    for (i = 0; i < field->data_size; i++)
+	    {
+	        if (p[i] != 0)
+	        {
+	            return false;
+	        }
+	    }
+
+	    return true;
+	}
+}
+
+/* Encode a field with static or pointer allocation, i.e. one whose data
+ * is available to the encoder directly. */
+static bool checkreturn encode_basic_field(pb_ostream_t *stream,
+    const pb_field_t *field, const void *pData)
+{
+    pb_encoder_t func;
+    bool implicit_has;
+    const void *pSize = &implicit_has;
+    
+    func = PB_ENCODERS[PB_LTYPE(field->type)];
+    
+    if (field->size_offset)
+    {
+        /* Static optional, repeated or oneof field */
+        pSize = (const char*)pData + field->size_offset;
+    }
+    else if (PB_HTYPE(field->type) == PB_HTYPE_OPTIONAL)
+    {
+        /* Proto3 style field, optional but without explicit has_ field. */
+        implicit_has = !pb_check_proto3_default_value(field, pData);
+    }
+    else
+    {
+        /* Required field, always present */
+        implicit_has = true;
+    }
+
+    if (PB_ATYPE(field->type) == PB_ATYPE_POINTER)
+    {
+        /* pData is a pointer to the field, which contains pointer to
+         * the data. If the 2nd pointer is NULL, it is interpreted as if
+         * the has_field was false.
+         */
+        pData = *(const void* const*)pData;
+        implicit_has = (pData != NULL);
+    }
+
+    switch (PB_HTYPE(field->type))
+    {
+        case PB_HTYPE_REQUIRED:
+            if (!pData)
+                PB_RETURN_ERROR(stream, "missing required field");
+            if (!pb_encode_tag_for_field(stream, field))
+                return false;
+            if (!func(stream, field, pData))
+                return false;
+            break;
+        
+        case PB_HTYPE_OPTIONAL:
+            if (*(const bool*)pSize)
+            {
+                if (!pb_encode_tag_for_field(stream, field))
+                    return false;
+            
+                if (!func(stream, field, pData))
+                    return false;
+            }
+            break;
+        
+        case PB_HTYPE_REPEATED: {
+            pb_size_t count;
+            if (field->size_offset != 0) {
+                count = *(const pb_size_t*)pSize;
+            } else {
+                count = field->array_size;
+            }
+            if (!encode_array(stream, field, pData, count, func))
+                return false;
+            break;
+        }
+        
+        case PB_HTYPE_ONEOF:
+            if (*(const pb_size_t*)pSize == field->tag)
+            {
+                if (!pb_encode_tag_for_field(stream, field))
+                    return false;
+
+                if (!func(stream, field, pData))
+                    return false;
+            }
+            break;
+            
+        default:
+            PB_RETURN_ERROR(stream, "invalid field type");
+    }
+    
+    return true;
+}
+
+/* Encode a field with callback semantics. This means that a user function is
+ * called to provide and encode the actual data. */
+static bool checkreturn encode_callback_field(pb_ostream_t *stream,
+    const pb_field_t *field, const void *pData)
+{
+    const pb_callback_t *callback = (const pb_callback_t*)pData;
+    
+#ifdef PB_OLD_CALLBACK_STYLE
+    const void *arg = callback->arg;
+#else
+    void * const *arg = &(callback->arg);
+#endif    
+    
+    if (callback->funcs.encode != NULL)
+    {
+        if (!callback->funcs.encode(stream, field, arg))
+            PB_RETURN_ERROR(stream, "callback error");
+    }
+    return true;
+}
+
+/* Encode a single field of any callback or static type. */
+static bool checkreturn encode_field(pb_ostream_t *stream,
+    const pb_field_t *field, const void *pData)
+{
+    switch (PB_ATYPE(field->type))
+    {
+        case PB_ATYPE_STATIC:
+        case PB_ATYPE_POINTER:
+            return encode_basic_field(stream, field, pData);
+        
+        case PB_ATYPE_CALLBACK:
+            return encode_callback_field(stream, field, pData);
+        
+        default:
+            PB_RETURN_ERROR(stream, "invalid field type");
+    }
+}
+
+/* Default handler for extension fields. Expects to have a pb_field_t
+ * pointer in the extension->type->arg field. */
+static bool checkreturn default_extension_encoder(pb_ostream_t *stream,
+    const pb_extension_t *extension)
+{
+    const pb_field_t *field = (const pb_field_t*)extension->type->arg;
+    
+    if (PB_ATYPE(field->type) == PB_ATYPE_POINTER)
+    {
+        /* For pointer extensions, the pointer is stored directly
+         * in the extension structure. This avoids having an extra
+         * indirection. */
+        return encode_field(stream, field, &extension->dest);
+    }
+    else
+    {
+        return encode_field(stream, field, extension->dest);
+    }
+}
+
+/* Walk through all the registered extensions and give them a chance
+ * to encode themselves. */
+static bool checkreturn encode_extension_field(pb_ostream_t *stream,
+    const pb_field_t *field, const void *pData)
+{
+    const pb_extension_t *extension = *(const pb_extension_t* const *)pData;
+    PB_UNUSED(field);
+    
+    while (extension)
+    {
+        bool status;
+        if (extension->type->encode)
+            status = extension->type->encode(stream, extension);
+        else
+            status = default_extension_encoder(stream, extension);
+
+        if (!status)
+            return false;
+        
+        extension = extension->next;
+    }
+    
+    return true;
+}
+
+/*********************
+ * Encode all fields *
+ *********************/
+
+static void *pb_const_cast(const void *p)
+{
+    /* Note: this casts away const, in order to use the common field iterator
+     * logic for both encoding and decoding. */
+    union {
+        void *p1;
+        const void *p2;
+    } t;
+    t.p2 = p;
+    return t.p1;
+}
+
+bool checkreturn pb_encode(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct)
+{
+    pb_field_iter_t iter;
+    if (!pb_field_iter_begin(&iter, fields, pb_const_cast(src_struct)))
+        return true; /* Empty message type */
+    
+    do {
+        if (PB_LTYPE(iter.pos->type) == PB_LTYPE_EXTENSION)
+        {
+            /* Special case for the extension field placeholder */
+            if (!encode_extension_field(stream, iter.pos, iter.pData))
+                return false;
+        }
+        else
+        {
+            /* Regular field */
+            if (!encode_field(stream, iter.pos, iter.pData))
+                return false;
+        }
+    } while (pb_field_iter_next(&iter));
+    
+    return true;
+}
+
+bool pb_encode_delimited(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct)
+{
+    return pb_encode_submessage(stream, fields, src_struct);
+}
+
+bool pb_encode_nullterminated(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct)
+{
+    const pb_byte_t zero = 0;
+
+    if (!pb_encode(stream, fields, src_struct))
+        return false;
+
+    return pb_write(stream, &zero, 1);
+}
+
+bool pb_get_encoded_size(size_t *size, const pb_field_t fields[], const void *src_struct)
+{
+    pb_ostream_t stream = PB_OSTREAM_SIZING;
+    
+    if (!pb_encode(&stream, fields, src_struct))
+        return false;
+    
+    *size = stream.bytes_written;
+    return true;
+}
+
+/********************
+ * Helper functions *
+ ********************/
+
+#ifdef PB_WITHOUT_64BIT
+bool checkreturn pb_encode_negative_varint(pb_ostream_t *stream, pb_uint64_t value)
+{
+  pb_byte_t buffer[10];
+  size_t i = 0;
+  size_t compensation = 32;/* we need to compensate 32 bits all set to 1 */
+
+  while (value)
+  {
+    buffer[i] = (pb_byte_t)((value & 0x7F) | 0x80);
+    value >>= 7;
+    if (compensation)
+    {
+      /* re-set all the compensation bits we can or need */
+      size_t bits = compensation > 7 ? 7 : compensation;
+      value ^= (pb_uint64_t)((0xFFu >> (8 - bits)) << 25); /* set the number of bits needed on the lowest of the most significant 7 bits */
+      compensation -= bits;
+    }
+    i++;
+  }
+  buffer[i - 1] &= 0x7F; /* Unset top bit on last byte */
+
+  return pb_write(stream, buffer, i);
+}
+#endif
+
+bool checkreturn pb_encode_varint(pb_ostream_t *stream, pb_uint64_t value)
+{
+    pb_byte_t buffer[10];
+    size_t i = 0;
+    
+    if (value <= 0x7F)
+    {
+        pb_byte_t v = (pb_byte_t)value;
+        return pb_write(stream, &v, 1);
+    }
+    
+    while (value)
+    {
+        buffer[i] = (pb_byte_t)((value & 0x7F) | 0x80);
+        value >>= 7;
+        i++;
+    }
+    buffer[i-1] &= 0x7F; /* Unset top bit on last byte */
+    
+    return pb_write(stream, buffer, i);
+}
+
+bool checkreturn pb_encode_svarint(pb_ostream_t *stream, pb_int64_t value)
+{
+    pb_uint64_t zigzagged;
+    if (value < 0)
+        zigzagged = ~((pb_uint64_t)value << 1);
+    else
+        zigzagged = (pb_uint64_t)value << 1;
+    
+    return pb_encode_varint(stream, zigzagged);
+}
+
+bool checkreturn pb_encode_fixed32(pb_ostream_t *stream, const void *value)
+{
+    uint32_t val = *(const uint32_t*)value;
+    pb_byte_t bytes[4];
+    bytes[0] = (pb_byte_t)(val & 0xFF);
+    bytes[1] = (pb_byte_t)((val >> 8) & 0xFF);
+    bytes[2] = (pb_byte_t)((val >> 16) & 0xFF);
+    bytes[3] = (pb_byte_t)((val >> 24) & 0xFF);
+    return pb_write(stream, bytes, 4);
+}
+
+#ifndef PB_WITHOUT_64BIT
+bool checkreturn pb_encode_fixed64(pb_ostream_t *stream, const void *value)
+{
+    uint64_t val = *(const uint64_t*)value;
+    pb_byte_t bytes[8];
+    bytes[0] = (pb_byte_t)(val & 0xFF);
+    bytes[1] = (pb_byte_t)((val >> 8) & 0xFF);
+    bytes[2] = (pb_byte_t)((val >> 16) & 0xFF);
+    bytes[3] = (pb_byte_t)((val >> 24) & 0xFF);
+    bytes[4] = (pb_byte_t)((val >> 32) & 0xFF);
+    bytes[5] = (pb_byte_t)((val >> 40) & 0xFF);
+    bytes[6] = (pb_byte_t)((val >> 48) & 0xFF);
+    bytes[7] = (pb_byte_t)((val >> 56) & 0xFF);
+    return pb_write(stream, bytes, 8);
+}
+#endif
+
+bool checkreturn pb_encode_tag(pb_ostream_t *stream, pb_wire_type_t wiretype, uint32_t field_number)
+{
+    pb_uint64_t tag = ((pb_uint64_t)field_number << 3) | wiretype;
+    return pb_encode_varint(stream, tag);
+}
+
+bool checkreturn pb_encode_tag_for_field(pb_ostream_t *stream, const pb_field_t *field)
+{
+    pb_wire_type_t wiretype;
+    switch (PB_LTYPE(field->type))
+    {
+        case PB_LTYPE_VARINT:
+        case PB_LTYPE_UVARINT:
+        case PB_LTYPE_SVARINT:
+            wiretype = PB_WT_VARINT;
+            break;
+        
+        case PB_LTYPE_FIXED32:
+            wiretype = PB_WT_32BIT;
+            break;
+        
+        case PB_LTYPE_FIXED64:
+            wiretype = PB_WT_64BIT;
+            break;
+        
+        case PB_LTYPE_BYTES:
+        case PB_LTYPE_STRING:
+        case PB_LTYPE_SUBMESSAGE:
+        case PB_LTYPE_FIXED_LENGTH_BYTES:
+            wiretype = PB_WT_STRING;
+            break;
+        
+        default:
+            PB_RETURN_ERROR(stream, "invalid field type");
+    }
+    
+    return pb_encode_tag(stream, wiretype, field->tag);
+}
+
+bool checkreturn pb_encode_string(pb_ostream_t *stream, const pb_byte_t *buffer, size_t size)
+{
+    if (!pb_encode_varint(stream, (pb_uint64_t)size))
+        return false;
+    
+    return pb_write(stream, buffer, size);
+}
+
+bool checkreturn pb_encode_submessage(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct)
+{
+    /* First calculate the message size using a non-writing substream. */
+    pb_ostream_t substream = PB_OSTREAM_SIZING;
+    size_t size;
+    bool status;
+    
+    if (!pb_encode(&substream, fields, src_struct))
+    {
+#ifndef PB_NO_ERRMSG
+        stream->errmsg = substream.errmsg;
+#endif
+        return false;
+    }
+    
+    size = substream.bytes_written;
+    
+    if (!pb_encode_varint(stream, (pb_uint64_t)size))
+        return false;
+    
+    if (stream->callback == NULL)
+        return pb_write(stream, NULL, size); /* Just sizing */
+    
+    if (stream->bytes_written + size > stream->max_size)
+        PB_RETURN_ERROR(stream, "stream full");
+        
+    /* Use a substream to verify that a callback doesn't write more than
+     * what it did the first time. */
+    substream.callback = stream->callback;
+    substream.state = stream->state;
+    substream.max_size = size;
+    substream.bytes_written = 0;
+#ifndef PB_NO_ERRMSG
+    substream.errmsg = NULL;
+#endif
+    
+    status = pb_encode(&substream, fields, src_struct);
+    
+    stream->bytes_written += substream.bytes_written;
+    stream->state = substream.state;
+#ifndef PB_NO_ERRMSG
+    stream->errmsg = substream.errmsg;
+#endif
+    
+    if (substream.bytes_written != size)
+        PB_RETURN_ERROR(stream, "submsg size changed");
+    
+    return status;
+}
+
+/* Field encoders */
+
+static bool checkreturn pb_enc_varint(pb_ostream_t *stream, const pb_field_t *field, const void *src)
+{
+    pb_int64_t value = 0;
+    
+    if (field->data_size == sizeof(int_least8_t))
+        value = *(const int_least8_t*)src;
+    else if (field->data_size == sizeof(int_least16_t))
+        value = *(const int_least16_t*)src;
+    else if (field->data_size == sizeof(int32_t))
+        value = *(const int32_t*)src;
+    else if (field->data_size == sizeof(pb_int64_t))
+        value = *(const pb_int64_t*)src;
+    else
+        PB_RETURN_ERROR(stream, "invalid data_size");
+    
+#ifdef PB_WITHOUT_64BIT
+    if (value < 0)
+      return pb_encode_negative_varint(stream, (pb_uint64_t)value);
+    else
+#endif
+      return pb_encode_varint(stream, (pb_uint64_t)value);
+}
+
+static bool checkreturn pb_enc_uvarint(pb_ostream_t *stream, const pb_field_t *field, const void *src)
+{
+    pb_uint64_t value = 0;
+    
+    if (field->data_size == sizeof(uint_least8_t))
+        value = *(const uint_least8_t*)src;
+    else if (field->data_size == sizeof(uint_least16_t))
+        value = *(const uint_least16_t*)src;
+    else if (field->data_size == sizeof(uint32_t))
+        value = *(const uint32_t*)src;
+    else if (field->data_size == sizeof(pb_uint64_t))
+        value = *(const pb_uint64_t*)src;
+    else
+        PB_RETURN_ERROR(stream, "invalid data_size");
+    
+    return pb_encode_varint(stream, value);
+}
+
+static bool checkreturn pb_enc_svarint(pb_ostream_t *stream, const pb_field_t *field, const void *src)
+{
+    pb_int64_t value = 0;
+    
+    if (field->data_size == sizeof(int_least8_t))
+        value = *(const int_least8_t*)src;
+    else if (field->data_size == sizeof(int_least16_t))
+        value = *(const int_least16_t*)src;
+    else if (field->data_size == sizeof(int32_t))
+        value = *(const int32_t*)src;
+    else if (field->data_size == sizeof(pb_int64_t))
+        value = *(const pb_int64_t*)src;
+    else
+        PB_RETURN_ERROR(stream, "invalid data_size");
+    
+    return pb_encode_svarint(stream, value);
+}
+
+static bool checkreturn pb_enc_fixed64(pb_ostream_t *stream, const pb_field_t *field, const void *src)
+{
+    PB_UNUSED(field);
+#ifndef PB_WITHOUT_64BIT
+    return pb_encode_fixed64(stream, src);
+#else
+    PB_UNUSED(src);
+    PB_RETURN_ERROR(stream, "no 64bit support");
+#endif
+}
+
+static bool checkreturn pb_enc_fixed32(pb_ostream_t *stream, const pb_field_t *field, const void *src)
+{
+    PB_UNUSED(field);
+    return pb_encode_fixed32(stream, src);
+}
+
+static bool checkreturn pb_enc_bytes(pb_ostream_t *stream, const pb_field_t *field, const void *src)
+{
+    const pb_bytes_array_t *bytes = NULL;
+
+    bytes = (const pb_bytes_array_t*)src;
+    
+    if (src == NULL)
+    {
+        /* Treat null pointer as an empty bytes field */
+        return pb_encode_string(stream, NULL, 0);
+    }
+    
+    if (PB_ATYPE(field->type) == PB_ATYPE_STATIC &&
+        PB_BYTES_ARRAY_T_ALLOCSIZE(bytes->size) > field->data_size)
+    {
+        PB_RETURN_ERROR(stream, "bytes size exceeded");
+    }
+    
+    return pb_encode_string(stream, bytes->bytes, bytes->size);
+}
+
+static bool checkreturn pb_enc_string(pb_ostream_t *stream, const pb_field_t *field, const void *src)
+{
+    size_t size = 0;
+    size_t max_size = field->data_size;
+    const char *p = (const char*)src;
+    
+    if (PB_ATYPE(field->type) == PB_ATYPE_POINTER)
+        max_size = (size_t)-1;
+
+    if (src == NULL)
+    {
+        size = 0; /* Treat null pointer as an empty string */
+    }
+    else
+    {
+        /* strnlen() is not always available, so just use a loop */
+        while (size < max_size && *p != '\0')
+        {
+            size++;
+            p++;
+        }
+    }
+
+    return pb_encode_string(stream, (const pb_byte_t*)src, size);
+}
+
+static bool checkreturn pb_enc_submessage(pb_ostream_t *stream, const pb_field_t *field, const void *src)
+{
+    if (field->ptr == NULL)
+        PB_RETURN_ERROR(stream, "invalid field descriptor");
+    
+    return pb_encode_submessage(stream, (const pb_field_t*)field->ptr, src);
+}
+
+static bool checkreturn pb_enc_fixed_length_bytes(pb_ostream_t *stream, const pb_field_t *field, const void *src)
+{
+    return pb_encode_string(stream, (const pb_byte_t*)src, field->data_size);
+}
+