Thrift: Generate structural fingerprints for thrift structs.

Summary:
We are going to write a dense protocol soon that eliminates some metadata.
To prevent version conflicts, we want each structure to have a
structural fingerprint that will change whenever the struct changes
in a way that will affect the dense protocol.
This change computes those fingerprints and puts them in
the generated C++ code.

Reviewed By: aditya, mcslee

Test Plan:
Recompiled thrift.
Thrifted DebugProtoTest with old and new compilers.
Compared output.
Also ran thrift with those "cout"s uncommented,
examined the fingerprint material,
and verified the hashes.

Revert Plan: ok


git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@665227 13f79535-47bb-0310-9956-ffa450edef68

compiler/cpp/Makefile.am

@@ -7,6 +7,7 @@ thrift_OBJDIR = obj
 thrift_SOURCES = src/thrifty.yy \
                  src/thriftl.ll \
                  src/main.cc \
+                 src/md5c.c \
                  src/generate/t_generator.cc \
                  src/generate/t_cpp_generator.cc \
                  src/generate/t_java_generator.cc \

compiler/cpp/src/generate/t_cpp_generator.cc

@@ -377,6 +377,20 @@ void t_cpp_generator::generate_struct_definition(ofstream& out,
     endl;
   indent_up();
 
+  // Put the fingerprint up top for all to see.
+  if (tstruct->has_fingerprint()) {
+    out <<
+      indent() << "static char* ascii_fingerprint = \"" <<
+        tstruct->get_ascii_fingerprint() << "\";" << endl <<
+      indent() << "static char binary_fingerprint[] = {";
+    char* comma = "";
+    for (int i = 0; i < t_struct::fingerprint_len; i++) {
+      out << comma << "0x" << t_struct::byte_to_hex(tstruct->get_binary_fingerprint()[i]);
+      comma = ",";
+    }
+    out << "};" << endl << endl;
+  }
+
   // Get members
   vector<t_field*>::const_iterator m_iter; 
   const vector<t_field*>& members = tstruct->get_members();

compiler/cpp/src/main.cc

@@ -513,6 +513,27 @@ void dump_docstrings(t_program* program) {
   }
 }
 
+/**
+ * Call generate_fingerprint for every structure.
+ */
+void generate_all_fingerprints(t_program* program) {
+  const vector<t_struct*>& structs = program->get_structs();
+  vector<t_struct*>::const_iterator s_iter;
+  for (s_iter = structs.begin(); s_iter != structs.end(); ++s_iter) {
+    t_struct* st = *s_iter;
+    st->generate_fingerprint();
+  }
+
+  // If you want to generate fingerprints for implicit structures, start here.
+  /*
+  const vector<t_service*>& services = program->get_services();
+  vector<t_service*>::const_iterator v_iter;
+  for (v_iter = services.begin(); v_iter != services.end(); ++v_iter) {
+    t_service* sv = *v_iter;
+  }
+  */
+}
+
 /**
  * Diplays the usage message and then exits with an error code.
  */
@@ -740,6 +761,9 @@ void generate(t_program* program) {
   try {
     pverbose("Program: %s\n", program->get_path().c_str());
 
+    // Compute fingerprints.
+    generate_all_fingerprints(program);
+
     if (gen_cpp) {
       pverbose("Generating C++\n");
       t_cpp_generator* cpp = new t_cpp_generator(program);

compiler/cpp/src/md5.h

@@ -0,0 +1,45 @@
+/* MD5.H - header file for MD5C.C
+ *
+ * This file has been modified for use in Thrift.
+ */
+
+/* Copyright (C) 1991-2, RSA Data Security, Inc. Created 1991. All
+rights reserved.
+
+License to copy and use this software is granted provided that it
+is identified as the "RSA Data Security, Inc. MD5 Message-Digest
+Algorithm" in all material mentioning or referencing this software
+or this function.
+
+License is also granted to make and use derivative works provided
+that such works are identified as "derived from the RSA Data
+Security, Inc. MD5 Message-Digest Algorithm" in all material
+mentioning or referencing the derived work.
+
+RSA Data Security, Inc. makes no representations concerning either
+the merchantability of this software or the suitability of this
+software for any particular purpose. It is provided "as is"
+without express or implied warranty of any kind.
+
+These notices must be retained in any copies of any part of this
+documentation and/or software.
+ */
+
+#include <stdint.h>
+
+/* MD5 context. */
+typedef struct {
+  uint32_t state[4];                                   /* state (ABCD) */
+  uint32_t count[2];        /* number of bits, modulo 2^64 (lsb first) */
+  unsigned char buffer[64];                            /* input buffer */
+} MD5_CTX;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+void MD5Init(MD5_CTX *);
+void MD5Update(MD5_CTX *, unsigned char *, unsigned int);
+void MD5Final(unsigned char [16], MD5_CTX *);
+#ifdef __cplusplus
+}
+#endif

compiler/cpp/src/md5c.c

@@ -0,0 +1,354 @@
+/* MD5C.C - RSA Data Security, Inc., MD5 message-digest algorithm
+ *
+ * This file has been modified for use in Thrift.
+ */
+
+/* Copyright (C) 1991-2, RSA Data Security, Inc. Created 1991. All
+   rights reserved.
+
+   License to copy and use this software is granted provided that it
+   is identified as the "RSA Data Security, Inc. MD5 Message-Digest
+   Algorithm" in all material mentioning or referencing this software
+   or this function.
+
+   License is also granted to make and use derivative works provided
+   that such works are identified as "derived from the RSA Data
+   Security, Inc. MD5 Message-Digest Algorithm" in all material
+   mentioning or referencing the derived work.
+
+   RSA Data Security, Inc. makes no representations concerning either
+   the merchantability of this software or the suitability of this
+   software for any particular purpose. It is provided "as is"
+   without express or implied warranty of any kind.
+
+   These notices must be retained in any copies of any part of this
+   documentation and/or software.
+ */
+
+#include "md5.h"
+
+/* GLOBAL.H - RSAREF types and constants
+ */
+
+/* POINTER defines a generic pointer type */
+typedef unsigned char *POINTER;
+
+/* UINT2 defines a two byte word */
+typedef uint16_t UINT2;
+
+/* UINT4 defines a four byte word */
+typedef uint32_t UINT4;
+
+#define PROTO_LIST(list) list
+
+/* END GLOBAL.H
+ */
+
+
+/* Constants for MD5Transform routine.
+ */
+#define S11 7
+#define S12 12
+#define S13 17
+#define S14 22
+#define S21 5
+#define S22 9
+#define S23 14
+#define S24 20
+#define S31 4
+#define S32 11
+#define S33 16
+#define S34 23
+#define S41 6
+#define S42 10
+#define S43 15
+#define S44 21
+
+static void MD5Transform PROTO_LIST ((UINT4 [4], unsigned char [64]));
+static void Encode PROTO_LIST
+  ((unsigned char *, UINT4 *, unsigned int));
+static void Decode PROTO_LIST
+  ((UINT4 *, unsigned char *, unsigned int));
+static void MD5_memcpy PROTO_LIST ((POINTER, POINTER, unsigned int));
+static void MD5_memset PROTO_LIST ((POINTER, int, unsigned int));
+
+static unsigned char PADDING[64] = {
+  0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+};
+
+/* F, G, H and I are basic MD5 functions.
+ */
+#define F(x, y, z) (((x) & (y)) | ((~x) & (z)))
+#define G(x, y, z) (((x) & (z)) | ((y) & (~z)))
+#define H(x, y, z) ((x) ^ (y) ^ (z))
+#define I(x, y, z) ((y) ^ ((x) | (~z)))
+
+/* ROTATE_LEFT rotates x left n bits.
+ */
+#define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32-(n))))
+
+/* FF, GG, HH, and II transformations for rounds 1, 2, 3, and 4.
+   Rotation is separate from addition to prevent recomputation.
+ */
+#define FF(a, b, c, d, x, s, ac) { \
+    (a) += F ((b), (c), (d)) + (x) + (UINT4)(ac); \
+    (a) = ROTATE_LEFT ((a), (s)); \
+    (a) += (b); \
+  }
+#define GG(a, b, c, d, x, s, ac) { \
+    (a) += G ((b), (c), (d)) + (x) + (UINT4)(ac); \
+    (a) = ROTATE_LEFT ((a), (s)); \
+    (a) += (b); \
+  }
+#define HH(a, b, c, d, x, s, ac) { \
+    (a) += H ((b), (c), (d)) + (x) + (UINT4)(ac); \
+    (a) = ROTATE_LEFT ((a), (s)); \
+    (a) += (b); \
+  }
+#define II(a, b, c, d, x, s, ac) { \
+    (a) += I ((b), (c), (d)) + (x) + (UINT4)(ac); \
+    (a) = ROTATE_LEFT ((a), (s)); \
+    (a) += (b); \
+  }
+
+/* MD5 initialization. Begins an MD5 operation, writing a new context.
+ */
+void MD5Init (context)
+MD5_CTX *context;                                        /* context */
+{
+  context->count[0] = context->count[1] = 0;
+
+  /* Load magic initialization constants.
+   */
+  context->state[0] = 0x67452301;
+  context->state[1] = 0xefcdab89;
+  context->state[2] = 0x98badcfe;
+  context->state[3] = 0x10325476;
+}
+
+/* MD5 block update operation. Continues an MD5 message-digest
+   operation, processing another message block, and updating the
+   context.
+ */
+void MD5Update (context, input, inputLen)
+MD5_CTX *context;                                        /* context */
+unsigned char *input;                                /* input block */
+unsigned int inputLen;                     /* length of input block */
+{
+  unsigned int i, index, partLen;
+
+  /* Compute number of bytes mod 64 */
+  index = (unsigned int)((context->count[0] >> 3) & 0x3F);
+
+  /* Update number of bits */
+  if ((context->count[0] += ((UINT4)inputLen << 3))
+      < ((UINT4)inputLen << 3))
+    context->count[1]++;
+  context->count[1] += ((UINT4)inputLen >> 29);
+
+  partLen = 64 - index;
+
+  /* Transform as many times as possible.
+   */
+  if (inputLen >= partLen) {
+    MD5_memcpy
+      ((POINTER)&context->buffer[index], (POINTER)input, partLen);
+    MD5Transform (context->state, context->buffer);
+
+    for (i = partLen; i + 63 < inputLen; i += 64)
+      MD5Transform (context->state, &input[i]);
+
+    index = 0;
+  }
+  else
+    i = 0;
+
+  /* Buffer remaining input */
+  MD5_memcpy
+    ((POINTER)&context->buffer[index], (POINTER)&input[i],
+     inputLen-i);
+}
+
+/* MD5 finalization. Ends an MD5 message-digest operation, writing the
+   the message digest and zeroizing the context.
+ */
+void MD5Final (digest, context)
+unsigned char digest[16];                         /* message digest */
+MD5_CTX *context;                                       /* context */
+{
+  unsigned char bits[8];
+  unsigned int index, padLen;
+
+  /* Save number of bits */
+  Encode (bits, context->count, 8);
+
+  /* Pad out to 56 mod 64.
+   */
+  index = (unsigned int)((context->count[0] >> 3) & 0x3f);
+  padLen = (index < 56) ? (56 - index) : (120 - index);
+  MD5Update (context, PADDING, padLen);
+
+  /* Append length (before padding) */
+  MD5Update (context, bits, 8);
+
+  /* Store state in digest */
+  Encode (digest, context->state, 16);
+
+  /* Zeroize sensitive information.
+   */
+  MD5_memset ((POINTER)context, 0, sizeof (*context));
+}
+
+/* MD5 basic transformation. Transforms state based on block.
+ */
+static void MD5Transform (state, block)
+UINT4 state[4];
+unsigned char block[64];
+{
+  UINT4 a = state[0], b = state[1], c = state[2], d = state[3], x[16];
+
+  Decode (x, block, 64);
+
+  /* Round 1 */
+  FF (a, b, c, d, x[ 0], S11, 0xd76aa478); /* 1 */
+  FF (d, a, b, c, x[ 1], S12, 0xe8c7b756); /* 2 */
+  FF (c, d, a, b, x[ 2], S13, 0x242070db); /* 3 */
+  FF (b, c, d, a, x[ 3], S14, 0xc1bdceee); /* 4 */
+  FF (a, b, c, d, x[ 4], S11, 0xf57c0faf); /* 5 */
+  FF (d, a, b, c, x[ 5], S12, 0x4787c62a); /* 6 */
+  FF (c, d, a, b, x[ 6], S13, 0xa8304613); /* 7 */
+  FF (b, c, d, a, x[ 7], S14, 0xfd469501); /* 8 */
+  FF (a, b, c, d, x[ 8], S11, 0x698098d8); /* 9 */
+  FF (d, a, b, c, x[ 9], S12, 0x8b44f7af); /* 10 */
+  FF (c, d, a, b, x[10], S13, 0xffff5bb1); /* 11 */
+  FF (b, c, d, a, x[11], S14, 0x895cd7be); /* 12 */
+  FF (a, b, c, d, x[12], S11, 0x6b901122); /* 13 */
+  FF (d, a, b, c, x[13], S12, 0xfd987193); /* 14 */
+  FF (c, d, a, b, x[14], S13, 0xa679438e); /* 15 */
+  FF (b, c, d, a, x[15], S14, 0x49b40821); /* 16 */
+
+  /* Round 2 */
+  GG (a, b, c, d, x[ 1], S21, 0xf61e2562); /* 17 */
+  GG (d, a, b, c, x[ 6], S22, 0xc040b340); /* 18 */
+  GG (c, d, a, b, x[11], S23, 0x265e5a51); /* 19 */
+  GG (b, c, d, a, x[ 0], S24, 0xe9b6c7aa); /* 20 */
+  GG (a, b, c, d, x[ 5], S21, 0xd62f105d); /* 21 */
+  GG (d, a, b, c, x[10], S22,  0x2441453); /* 22 */
+  GG (c, d, a, b, x[15], S23, 0xd8a1e681); /* 23 */
+  GG (b, c, d, a, x[ 4], S24, 0xe7d3fbc8); /* 24 */
+  GG (a, b, c, d, x[ 9], S21, 0x21e1cde6); /* 25 */
+  GG (d, a, b, c, x[14], S22, 0xc33707d6); /* 26 */
+  GG (c, d, a, b, x[ 3], S23, 0xf4d50d87); /* 27 */
+  GG (b, c, d, a, x[ 8], S24, 0x455a14ed); /* 28 */
+  GG (a, b, c, d, x[13], S21, 0xa9e3e905); /* 29 */
+  GG (d, a, b, c, x[ 2], S22, 0xfcefa3f8); /* 30 */
+  GG (c, d, a, b, x[ 7], S23, 0x676f02d9); /* 31 */
+  GG (b, c, d, a, x[12], S24, 0x8d2a4c8a); /* 32 */
+
+  /* Round 3 */
+  HH (a, b, c, d, x[ 5], S31, 0xfffa3942); /* 33 */
+  HH (d, a, b, c, x[ 8], S32, 0x8771f681); /* 34 */
+  HH (c, d, a, b, x[11], S33, 0x6d9d6122); /* 35 */
+  HH (b, c, d, a, x[14], S34, 0xfde5380c); /* 36 */
+  HH (a, b, c, d, x[ 1], S31, 0xa4beea44); /* 37 */
+  HH (d, a, b, c, x[ 4], S32, 0x4bdecfa9); /* 38 */
+  HH (c, d, a, b, x[ 7], S33, 0xf6bb4b60); /* 39 */
+  HH (b, c, d, a, x[10], S34, 0xbebfbc70); /* 40 */
+  HH (a, b, c, d, x[13], S31, 0x289b7ec6); /* 41 */
+  HH (d, a, b, c, x[ 0], S32, 0xeaa127fa); /* 42 */
+  HH (c, d, a, b, x[ 3], S33, 0xd4ef3085); /* 43 */
+  HH (b, c, d, a, x[ 6], S34,  0x4881d05); /* 44 */
+  HH (a, b, c, d, x[ 9], S31, 0xd9d4d039); /* 45 */
+  HH (d, a, b, c, x[12], S32, 0xe6db99e5); /* 46 */
+  HH (c, d, a, b, x[15], S33, 0x1fa27cf8); /* 47 */
+  HH (b, c, d, a, x[ 2], S34, 0xc4ac5665); /* 48 */
+
+  /* Round 4 */
+  II (a, b, c, d, x[ 0], S41, 0xf4292244); /* 49 */
+  II (d, a, b, c, x[ 7], S42, 0x432aff97); /* 50 */
+  II (c, d, a, b, x[14], S43, 0xab9423a7); /* 51 */
+  II (b, c, d, a, x[ 5], S44, 0xfc93a039); /* 52 */
+  II (a, b, c, d, x[12], S41, 0x655b59c3); /* 53 */
+  II (d, a, b, c, x[ 3], S42, 0x8f0ccc92); /* 54 */
+  II (c, d, a, b, x[10], S43, 0xffeff47d); /* 55 */
+  II (b, c, d, a, x[ 1], S44, 0x85845dd1); /* 56 */
+  II (a, b, c, d, x[ 8], S41, 0x6fa87e4f); /* 57 */
+  II (d, a, b, c, x[15], S42, 0xfe2ce6e0); /* 58 */
+  II (c, d, a, b, x[ 6], S43, 0xa3014314); /* 59 */
+  II (b, c, d, a, x[13], S44, 0x4e0811a1); /* 60 */
+  II (a, b, c, d, x[ 4], S41, 0xf7537e82); /* 61 */
+  II (d, a, b, c, x[11], S42, 0xbd3af235); /* 62 */
+  II (c, d, a, b, x[ 2], S43, 0x2ad7d2bb); /* 63 */
+  II (b, c, d, a, x[ 9], S44, 0xeb86d391); /* 64 */
+
+  state[0] += a;
+  state[1] += b;
+  state[2] += c;
+  state[3] += d;
+
+  /* Zeroize sensitive information.
+   */
+  MD5_memset ((POINTER)x, 0, sizeof (x));
+}
+
+/* Encodes input (UINT4) into output (unsigned char). Assumes len is
+   a multiple of 4.
+ */
+static void Encode (output, input, len)
+unsigned char *output;
+UINT4 *input;
+unsigned int len;
+{
+  unsigned int i, j;
+
+  for (i = 0, j = 0; j < len; i++, j += 4) {
+    output[j] = (unsigned char)(input[i] & 0xff);
+    output[j+1] = (unsigned char)((input[i] >> 8) & 0xff);
+    output[j+2] = (unsigned char)((input[i] >> 16) & 0xff);
+    output[j+3] = (unsigned char)((input[i] >> 24) & 0xff);
+  }
+}
+
+/* Decodes input (unsigned char) into output (UINT4). Assumes len is
+   a multiple of 4.
+ */
+static void Decode (output, input, len)
+UINT4 *output;
+unsigned char *input;
+unsigned int len;
+{
+  unsigned int i, j;
+
+  for (i = 0, j = 0; j < len; i++, j += 4)
+    output[i] = ((UINT4)input[j]) | (((UINT4)input[j+1]) << 8) |
+      (((UINT4)input[j+2]) << 16) | (((UINT4)input[j+3]) << 24);
+}
+
+/* Note: Replace "for loop" with standard memcpy if possible.
+ */
+static void MD5_memcpy (output, input, len)
+POINTER output;
+POINTER input;
+unsigned int len;
+{
+  unsigned int i;
+
+  for (i = 0; i < len; i++)
+    output[i] = input[i];
+}
+
+/* Note: Replace "for loop" with standard memset if possible.
+ */
+static void MD5_memset (output, value, len)
+POINTER output;
+int value;
+unsigned int len;
+{
+  unsigned int i;
+
+  for (i = 0; i < len; i++)
+    ((char *)output)[i] = (char)value;
+}
+

compiler/cpp/src/parse/t_base_type.h

@@ -7,6 +7,7 @@
 #ifndef T_BASE_TYPE_H
 #define T_BASE_TYPE_H
 
+#include <cstdlib>
 #include "t_type.h"
 
 /**
@@ -84,7 +85,22 @@ class t_base_type : public t_type {
   bool is_base_type() const {
     return true;
   }
-    
+
+  virtual std::string get_fingerprint_material() const {
+    switch (base_) {
+      case TYPE_VOID   : return   "void"; break;
+      case TYPE_STRING : return "string"; break;
+      case TYPE_BOOL   : return   "bool"; break;
+      case TYPE_BYTE   : return   "byte"; break;
+      case TYPE_I16    : return    "i16"; break;
+      case TYPE_I32    : return    "i32"; break;
+      case TYPE_I64    : return    "164"; break;
+      case TYPE_DOUBLE : return "double"; break;
+      default:
+        throw "BUG: Can't get fingerprint material for this base type.";
+    }
+  }
+
  private:
   t_base base_;
 

compiler/cpp/src/parse/t_enum.h

@@ -36,6 +36,10 @@ class t_enum : public t_type {
     return true;
   }
 
+  virtual std::string get_fingerprint_material() const {
+    return "enum";
+  }
+
  private:
   std::vector<t_enum_value*> constants_;
 };

compiler/cpp/src/parse/t_field.h

@@ -8,6 +8,7 @@
 #define T_FIELD_H
 
 #include <string>
+#include <boost/lexical_cast.hpp>
 
 // Forward declare for xsd_attrs
 class t_struct;
@@ -112,6 +113,14 @@ class t_field {
     has_doc_ = true;                                          
   }                                                           
 
+  // This is not the same function as t_type::get_fingerprint_material,
+  // but it does the same thing.
+  std::string get_fingerprint_material() const {
+    return boost::lexical_cast<std::string>(key_) + ":" +
+      (req_ == OPTIONAL ? "opt-" : "") +
+      type_->get_fingerprint_material();
+  }
+
  private:
   t_type* type_;
   std::string name_;

compiler/cpp/src/parse/t_list.h

@@ -27,6 +27,10 @@ class t_list : public t_container {
     return true;
   }
 
+  virtual std::string get_fingerprint_material() const {
+    return "list<" + elem_type_->get_fingerprint_material() + ">";
+  }
+
  private:
   t_type* elem_type_;
 };

compiler/cpp/src/parse/t_map.h

@@ -33,6 +33,11 @@ class t_map : public t_container {
     return true;
   }
 
+  virtual std::string get_fingerprint_material() const {
+    return "map<" + key_type_->get_fingerprint_material() +
+      "," + val_type_->get_fingerprint_material() + ">";
+  }
+
  private:
   t_type* key_type_;
   t_type* val_type_;

compiler/cpp/src/parse/t_service.h

@@ -43,6 +43,11 @@ class t_service : public t_type {
     return extends_;
   }
 
+  virtual std::string get_fingerprint_material() const {
+    // Services should never be used in fingerprints.
+    throw "BUG: Can't get fingerprint material for service.";
+  }
+
  private:
   std::vector<t_function*> functions_;
   t_service* extends_;

compiler/cpp/src/parse/t_set.h

@@ -27,6 +27,10 @@ class t_set : public t_container {
     return true;
   }
 
+  virtual std::string get_fingerprint_material() const {
+    return "set<" + elem_type_->get_fingerprint_material() + ">";
+  }
+
  private:
   t_type* elem_type_;
 };

compiler/cpp/src/parse/t_struct.h

@@ -9,10 +9,14 @@
 
 #include <vector>
 #include <string>
+#include <cstring>
 
 #include "t_type.h"
 #include "t_field.h"
 
+// What's worse?  This, or making a src/parse/non_inlined.cc?
+#include "md5.h"
+
 // Forward declare that puppy
 class t_program;
 
@@ -27,12 +31,18 @@ class t_struct : public t_type {
   t_struct(t_program* program) :
     t_type(program),
     is_xception_(false),
-    xsd_all_(false) {}
+    xsd_all_(false)
+  {
+    memset(fingerprint_, 0, sizeof(fingerprint_));
+  }
 
   t_struct(t_program* program, const std::string& name) :
     t_type(program, name),
     is_xception_(false),
-    xsd_all_(false) {}
+    xsd_all_(false)
+  {
+    memset(fingerprint_, 0, sizeof(fingerprint_));
+  }
 
   void set_name(const std::string& name) {
     name_ = name;
@@ -66,12 +76,80 @@ class t_struct : public t_type {
     return is_xception_;
   }
 
+  virtual std::string get_fingerprint_material() const {
+    std::string rv = "{";
+    std::vector<t_field*>::const_iterator m_iter;
+    for (m_iter = members_.begin(); m_iter != members_.end(); ++m_iter) {
+      rv += (**m_iter).get_fingerprint_material();
+      rv += ";";
+    }
+    rv += "}";
+    return rv;
+  }
+
+  // Fingerprint should change whenever (and only when)
+  // the encoding via TDenseProtocol changes.
+  static const int fingerprint_len = 16;
+
+  // Call this before trying get_*_fingerprint().
+  void generate_fingerprint() {
+    std::string material = get_fingerprint_material();
+    MD5_CTX ctx;
+    MD5Init(&ctx);
+    MD5Update(&ctx, (unsigned char*)(material.data()), material.size());
+    MD5Final(fingerprint_, &ctx);
+    //std::cout << get_name() << std::endl;
+    //std::cout << material << std::endl;
+    //std::cout << get_ascii_fingerprint() << std::endl << std::endl;
+  }
+
+  bool has_fingerprint() const {
+    for (int i = 0; i < fingerprint_len; i++) {
+      if (fingerprint_[i] != 0) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  const uint8_t* get_binary_fingerprint() const {
+    return fingerprint_;
+  }
+
+  std::string get_ascii_fingerprint() const {
+    std::string rv;
+    const uint8_t* fp = get_binary_fingerprint();
+    for (int i = 0; i < fingerprint_len; i++) {
+      rv += byte_to_hex(fp[i]);
+    }
+    return rv;
+  }
+
+  // This function will break (maybe badly) unless 0 <= num <= 16.
+  static char nybble_to_xdigit(int num) {
+    if (num < 10) {
+      return '0' + num;
+    } else {
+      return 'A' + num - 10;
+    }
+  }
+
+  static std::string byte_to_hex(uint8_t byte) {
+    std::string rv;
+    rv += nybble_to_xdigit(byte >> 4);
+    rv += nybble_to_xdigit(byte & 0x0f);
+    return rv;
+  }
+
+
  private:
+
   std::vector<t_field*> members_;
   bool is_xception_;
 
   bool xsd_all_;
 
+  uint8_t fingerprint_[fingerprint_len];
 };
 
 #endif

compiler/cpp/src/parse/t_type.h

@@ -50,6 +50,11 @@ class t_type : public t_doc {
     return program_;
   }
 
+  // Return a string that uniquely identifies this type
+  // from any other thrift type in the world, as far as
+  // TDenseProtocol is concerned.
+  virtual std::string get_fingerprint_material() const = 0;
+
  protected:
   t_type() {}
 

compiler/cpp/src/parse/t_typedef.h

@@ -39,6 +39,10 @@ class t_typedef : public t_type {
     return true;
   }
 
+  virtual std::string get_fingerprint_material() const {
+    return type_->get_fingerprint_material();
+  }
+
  private:
   t_type* type_;
   std::string symbolic_;