SQLite

static void jsonAppendSeparator(JsonString *p){
  char c;
  if( p->nUsed==0 ) return;
  c = p->zBuf[p->nUsed-1];
  if( c=='[' || c=='{' ) return;
  jsonAppendChar(p, ',');
}

/* c is a control character.  Append the canonical JSON representation
** of that control character to p.
**
** This routine assumes that the output buffer has already been enlarged
** sufficiently to hold the worst-case encoding plus a nul terminator.
*/
static void jsonAppendControlChar(JsonString *p, u8 c){
  static const char aSpecial[] = {
     0, 0, 0, 0, 0, 0, 0, 0, 'b', 't', 'n', 0, 'f', 'r', 0, 0,
     0, 0, 0, 0, 0, 0, 0, 0,   0,   0,   0, 0,   0,   0, 0, 0
  };
  assert( sizeof(aSpecial)==32 );
  assert( aSpecial['\b']=='b' );
  assert( aSpecial['\f']=='f' );
  assert( aSpecial['\n']=='n' );
  assert( aSpecial['\r']=='r' );
  assert( aSpecial['\t']=='t' );
  assert( c>=0 && c<sizeof(aSpecial) );
  assert( p->nUsed+7 <= p->nAlloc );
  if( aSpecial[c] ){
    p->zBuf[p->nUsed] = '\\';
    p->zBuf[p->nUsed+1] = aSpecial[c];
    p->nUsed += 2;
  }else{
    p->zBuf[p->nUsed] = '\\';
    p->zBuf[p->nUsed+1] = 'u';
    p->zBuf[p->nUsed+2] = '0';
    p->zBuf[p->nUsed+3] = '0';
    p->zBuf[p->nUsed+4] = "0123456789abcdef"[c>>4];
    p->zBuf[p->nUsed+5] = "0123456789abcdef"[c&0xf];
    p->nUsed += 6;
  }
}

/* Append the N-byte string in zIn to the end of the JsonString string
** under construction.  Enclose the string in double-quotes ("...") and
** escape any double-quotes or backslash characters contained within the
** string.
**
** This routine is a high-runner.  There is a measurable performance

      memcpy(&p->zBuf[p->nUsed], z, k);
      p->nUsed += k;
      z += k;
      N -= k;
    }
    c = z[0];
    if( c=='"' || c=='\\' ){

      if( (p->nUsed+N+3 > p->nAlloc) && jsonStringGrow(p,N+3)!=0 ) return;
      p->zBuf[p->nUsed++] = '\\';
      p->zBuf[p->nUsed++] = c;
    }else if( c=='\'' ){
      p->zBuf[p->nUsed++] = c;
    }else{















      if( (p->nUsed+N+7 > p->nAlloc) && jsonStringGrow(p,N+7)!=0 ) return;






      jsonAppendControlChar(p, c);
    }
    z++;
    N--;
  }
  p->zBuf[p->nUsed++] = '"';
  assert( p->nUsed<p->nAlloc );
}

    case JSONB_TEXT5: {
      j = i+n;
      k = j+sz;
      while( j<k ){
        if( !jsonIsOk[z[j]] && z[j]!='\'' ){
          if( z[j]=='"' ){
            if( x==JSONB_TEXTJ ) return j+1;
          }else if( z[j]<=0x1f ){
            /* Control characters in JSON5 string literals are ok */
            if( x==JSONB_TEXTJ ) return j+1;
          }else if( NEVER(z[j]!='\\') || j+1>=k ){
            return j+1;
          }else if( strchr("\"\\/bfnrt",z[j+1])!=0 ){
            j++;
          }else if( z[j+1]=='u' ){
            if( j+5>=k ) return j+1;
            if( !jsonIs4Hex((const char*)&z[j+2]) ) return j+1;
            j++;

          opcode = JSONB_TEXT5;
          pParse->hasNonstd = 1;
        }else{
          pParse->iErr = j;
          return -1;
        }
      }else if( c<=0x1f ){
        if( c==0 ){
          pParse->iErr = j;
          return -1;
        }
        /* Control characters are not allowed in canonical JSON string
        ** literals, but are allowed in JSON5 string literals. */
        opcode = JSONB_TEXT5;
        pParse->hasNonstd = 1;
      }else if( c=='"' ){
        opcode = JSONB_TEXT5;
      }
      j++;
    }
    jsonBlobAppendNode(pParse, opcode, j-1-i, &z[i+1]);
    return j+1;

    case JSONB_TEXT5: {
      const char *zIn;
      u32 k;
      u32 sz2 = sz;
      zIn = (const char*)&pParse->aBlob[i+n];
      jsonAppendChar(pOut, '"');
      while( sz2>0 ){
        for(k=0; k<sz2 && (jsonIsOk[(u8)zIn[k]] || zIn[k]=='\''); k++){}
        if( k>0 ){
          jsonAppendRawNZ(pOut, zIn, k);
          if( k>=sz2 ){
            break;
          }
          zIn += k;
          sz2 -= k;
        }
        if( zIn[0]=='"' ){
          jsonAppendRawNZ(pOut, "\\\"", 2);
          zIn++;
          sz2--;
          continue;
        }
        if( zIn[0]<=0x1f ){
          if( pOut->nUsed+7>pOut->nAlloc && jsonStringGrow(pOut,7) ) break;
          jsonAppendControlChar(pOut, zIn[0]);
          zIn++;
          sz2--;
          continue;
        }
        assert( zIn[0]=='\\' );
        assert( sz2>=1 );
        if( sz2<2 ){
          pOut->eErr |= JSTRING_MALFORMED;

} xyz

# 2023-11-08 forum/forumpost/ddcad3e884
#
do_execsql_test 13.1 {
  SELECT json('{x:''a "b" c''}');
} {{{"x":"a \"b\" c"}}}

# 2024-01-31
# Allow control characters within JSON5 string literals.
#
for {set c 1} {$c<=0x1f} {incr c} {
  do_execsql_test 14.$c.1 {
    SELECT json_valid('"abc' || char($c) || 'xyz"');
  } {0}
  do_execsql_test 14.$c.2 {
    SELECT json_valid('"abc' || char($c) || 'xyz"', 2);
  } {1}
  switch $c {
    8   {set e "\\b"}
    9   {set e "\\t"}
    10  {set e "\\n"}
    12  {set e "\\f"}
    13  {set e "\\r"}
    default {set e [format "\\u00%02x" $c]}
  }
  do_execsql_test 14.$c.3 {
    SELECT json('{label:"abc' || char($c) || 'xyz"}');
  } "{{\"label\":\"abc${e}xyz\"}}"
  do_execsql_test 14.$c.4 {
    SELECT jsonb('{label:"abc' || char($c) || 'xyz"}') -> '$';
  } "{{\"label\":\"abc${e}xyz\"}}"
}


finish_test