Prototype implementation of the unistr() SQL function.

FossilOrigin-Name: 7cc302de05ed2a973372c05f55b048bf99af3d2590dd29f6fd0f379fb451aa0e

src/func.c

@@ -1149,6 +1149,132 @@ void sqlite3QuoteValue(StrAccum *pStr, sqlite3_value *pValue){
   }
 }
 
+/*
+** Write a single UTF8 character whose value if v into the
+** buffer starting at zOut.  Return the number of bytes needed
+** to encode that character.
+*/
+static int appendOneUtf8Char(char *zOut, u32 v){
+  if( v<0x00080 ){
+    zOut[0] = (u8)(v & 0xff);
+    return 1;
+  }
+  if( v<0x00800 ){
+    zOut[0] = 0xc0 + (u8)((v>>6) & 0x1f);
+    zOut[1] = 0x80 + (u8)(v & 0x3f);
+    return 2;
+  }
+  if( v<0x10000 ){
+    zOut[0] = 0xe0 + (u8)((v>>12) & 0x0f);
+    zOut[1] = 0x80 + (u8)((v>>6) & 0x3f);
+    zOut[2] = 0x80 + (u8)(v & 0x3f);
+    return 3;
+  }
+  zOut[0] = 0xf0 + (u8)((v>>18) & 0x07);
+  zOut[1] = 0x80 + (u8)((v>>12) & 0x3f);
+  zOut[2] = 0x80 + (u8)((v>>6) & 0x3f);
+  zOut[3] = 0x80 + (u8)(v & 0x3f);
+  return 4;
+}
+
+/*
+** Return true if z[] begins with N hexadecimal digits, and write
+** a decoding of those digits into *pVal.  Or return false if any
+** one of the first N characters in z[] is not a hexadecimal digit.
+*/
+static int isNHex(const char *z, int N, u32 *pVal){
+  int i;
+  int v = 0;
+  for(i=0; i<N; i++){
+    if( !sqlite3Isxdigit(z[i]) ) return 0;
+    v = (v<<4) + sqlite3HexToInt(z[i]);
+  }
+  *pVal = v;
+  return 1;
+}
+
+/*
+** Implementation of the UNISTR() function.
+**
+** This is intended to be a work-alike of the UNISTR() function in
+** PostgreSQL.  Quoting from the PG documentation (PostgreSQL 17 -
+** scraped on 2025-02-22):
+**
+**    Evaluate escaped Unicode characters in the argument. Unicode
+**    characters can be specified as \XXXX (4 hexadecimal digits),
+**    \+XXXXXX (6 hexadecimal digits), \uXXXX (4 hexadecimal digits),
+**    or \UXXXXXXXX (8 hexadecimal digits). To specify a backslash,
+**    write two backslashes. All other characters are taken literally.
+*/
+static void unistrFunc(
+  sqlite3_context *context,
+  int argc,
+  sqlite3_value **argv
+){
+  char *zOut;
+  const char *zIn;
+  int nIn;
+  int i, j, n;
+  u32 v;
+
+  assert( argc==1 );
+  zIn = (const char*)sqlite3_value_text(argv[0]);
+  if( zIn==0 ) return;
+  nIn = sqlite3_value_bytes(argv[0]);
+  zOut = sqlite3_malloc64(nIn+1);
+  if( zOut==0 ){
+    sqlite3_result_error_nomem(context);
+    return;
+  }
+  i = j = 0;
+  while( i<nIn ){
+    char *z = strchr(&zIn[i],'\\');
+    if( z==0 ){
+      n = nIn - i;
+      memmove(&zOut[j], &zIn[i], n);
+      j += n;
+      break;
+    }
+    n = z - &zIn[i];
+    if( n>0 ){
+      memmove(&zOut[j], &zIn[i], n);
+      j += n;
+      i += n;
+    }
+    if( zIn[i+1]=='\\' ){
+      i += 2;
+      zOut[j++] = '\\';
+    }else if( sqlite3Isxdigit(zIn[i+1]) ){
+      if( !isNHex(&zIn[i+1], 4, &v) ) goto unistr_error;
+      i += 5;
+      j += appendOneUtf8Char(&zOut[j], v);
+    }else if( zIn[i+1]=='+' ){
+      if( !isNHex(&zIn[i+2], 6, &v) ) goto unistr_error;
+      i += 8;
+      j += appendOneUtf8Char(&zOut[j], v);
+    }else if( zIn[i+1]=='u' ){
+      if( !isNHex(&zIn[i+2], 4, &v) ) goto unistr_error;
+      i += 6;
+      j += appendOneUtf8Char(&zOut[j], v);
+    }else if( zIn[i+1]=='U' ){
+      if( !isNHex(&zIn[i+2], 8, &v) ) goto unistr_error;
+      i += 10;
+      j += appendOneUtf8Char(&zOut[j], v);
+    }else{
+      goto unistr_error;
+    }
+  }
+  zOut[j] = 0;
+  sqlite3_result_text64(context, zOut, j, sqlite3_free, SQLITE_UTF8);
+  return;
+
+unistr_error:
+  sqlite3_free(zOut);
+  sqlite3_result_error(context, "invalid Unicode escape", -1);
+  return;
+}
+
+
 /*
 ** Implementation of the QUOTE() function. 
 **
@@ -2736,6 +2862,7 @@ void sqlite3RegisterBuiltinFunctions(void){
     DFUNCTION(sqlite_version,    0, 0, 0, versionFunc      ),
     DFUNCTION(sqlite_source_id,  0, 0, 0, sourceidFunc     ),
     FUNCTION(sqlite_log,         2, 0, 0, errlogFunc       ),
+    FUNCTION(unistr,             1, 0, 0, unistrFunc       ),
     FUNCTION(quote,              1, 0, 0, quoteFunc        ),
     VFUNCTION(last_insert_rowid, 0, 0, 0, last_insert_rowid),
     VFUNCTION(changes,           0, 0, 0, changes          ),