feat: add custom delimiter to csv_agg

Addresses the problem on PostgREST/postgrest#1102

Adds an overloaded `csv_agg` function:

```sql
SELECT csv_agg(x, '|') AS body
FROM   projects x;
```

Author: steve-chavez

.github/workflows/ci.yaml

@@ -37,7 +37,7 @@ jobs:
   loadtest:
     strategy:
       matrix:
-        kind: ['csv_agg', 'postgrest']
+        kind: ['csv_agg', 'csv_agg_delim', 'postgrest']
     name: Loadtest
     runs-on: ubuntu-24.04
     steps:

.gitignore

@@ -7,3 +7,4 @@ results/
 *.diffs
 pgbench_log.*
 .history
+pg_csv--*.sql

README.md

@@ -4,11 +4,25 @@
 [![Coverage Status](https://coveralls.io/repos/github/PostgREST/pg_csv/badge.svg)](https://coveralls.io/github/PostgREST/pg_csv)
 [![Tests](https://github.com/PostgREST/pg_csv/actions/workflows/ci.yaml/badge.svg)](https://github.com/PostgREST/pg_csv/actions)
 
+## Installation
+
+Clone this repo and run:
+
+```bash
+make && make install
+```
+
+To install the extension:
+
+```psql
+create extension pg_csv;
+```
+
 ## csv_agg
 
 Aggregate that builds a CSV as per [RFC 4180](https://www.ietf.org/rfc/rfc4180.txt), quoting as required.
 
-```
+```psql
 select csv_agg(x) from projects x;
       csv_agg
 -------------------
@@ -20,3 +34,21 @@ select csv_agg(x) from projects x;
  5,Orphan,
 (1 row)
 ```
+
+It also supports adding a custom delimiter.
+
+```psql
+select csv_agg(x, '|') from projects x;
+      csv_agg
+-------------------
+ id|name|client_id+
+ 1|Windows 7|1    +
+ 2|Windows 10|1   +
+ 3|IOS|2          +
+ 4|OSX|2          +
+ 5|Orphan|
+(1 row)
+```
+
+> [!IMPORTANT]
+> Newline, carriage return and double quotes are not supported as delimiters to maintain the integrity of the separated values format.

bench/csv_agg_delim.sql

@@ -0,0 +1,5 @@
+\set lim random(1000, 2000)
+
+select csv_agg(t,'|') from (
+  select * from student_emotion_assessments limit :lim
+) as t;

sql/pg_csv--0.1.sql

@@ -3,13 +3,26 @@ create function csv_agg_transfn(internal, anyelement)
   language c
   as 'pg_csv';
 
+create function csv_agg_transfn(internal, anyelement, "char")
+  returns internal
+  language c
+  as 'pg_csv';
+
 create function csv_agg_finalfn(internal)
   returns text
   language c
   as 'pg_csv';
 
+create aggregate csv_agg(anyelement, "char") (
+  sfunc     = csv_agg_transfn,
+  stype     = internal,
+  finalfunc = csv_agg_finalfn,
+  parallel  = safe
+);
+
 create aggregate csv_agg(anyelement) (
-  sfunc      = csv_agg_transfn,
-  stype      = internal,
-  finalfunc  = csv_agg_finalfn
+  sfunc     = csv_agg_transfn,
+  stype     = internal,
+  finalfunc = csv_agg_finalfn,
+  parallel  = safe
 );

sql/pg_csv.sql

@@ -2,10 +2,9 @@
 
 PG_MODULE_MAGIC;
 
-static const char NEWLINE   = '\n';
-static const char DELIMITER = ',';
-static const char DQUOTE    = '"';
-static const char CR        = '\r';
+static const char NEWLINE = '\n';
+static const char DQUOTE  = '"';
+static const char CR      = '\r';
 
 typedef struct {
   StringInfoData accum_buf;
@@ -14,17 +13,21 @@ typedef struct {
   TupleDesc      tupdesc;
 } CsvAggState;
 
+static inline bool is_reserved(char c) {
+  return c == DQUOTE || c == NEWLINE || c == CR;
+}
+
 // Any comma, quote, CR, LF requires quoting as per RFC https://www.ietf.org/rfc/rfc4180.txt
-static inline bool needs_quote(const char *s, size_t n) {
+static inline bool needs_quote(const char *s, size_t n, char delim) {
   while (n--) {
     char c = *s++;
-    if (c == DELIMITER || c == DQUOTE || c == NEWLINE || c == CR) return true;
+    if (c == delim || is_reserved(c)) return true;
   }
   return false;
 }
 
-static inline void csv_append_field(StringInfo buf, const char *s, size_t n) {
-  if (!needs_quote(s, n)) {
+static inline void csv_append_field(StringInfo buf, const char *s, size_t n, char delim) {
+  if (!needs_quote(s, n, delim)) {
     appendBinaryStringInfo(buf, s, n);
   } else {
     appendStringInfoChar(buf, DQUOTE);
@@ -72,6 +75,10 @@ Datum csv_agg_transfn(PG_FUNCTION_ARGS) {
 
   HeapTupleHeader next = PG_GETARG_HEAPTUPLEHEADER(1);
 
+  char delim = PG_NARGS() >= 3 && !PG_ARGISNULL(2) ? PG_GETARG_CHAR(2) : ',';
+
+  if (is_reserved(delim)) ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE), errmsg("delimiter cannot be newline, carriage return or double quote")));
+
   // build header and cache tupdesc once
   if (!state->header_done) {
     TupleDesc tdesc = lookup_rowtype_tupdesc(HeapTupleHeaderGetTypeId(next), HeapTupleHeaderGetTypMod(next));
@@ -83,10 +90,10 @@ Datum csv_agg_transfn(PG_FUNCTION_ARGS) {
         continue;
 
       if (i > 0) // only append delimiter after the first value
-        appendStringInfoChar(&state->accum_buf, DELIMITER);
+        appendStringInfoChar(&state->accum_buf, delim);
 
       char *cstr = NameStr(att->attname);
-      csv_append_field(&state->accum_buf, cstr, strlen(cstr));
+      csv_append_field(&state->accum_buf, cstr, strlen(cstr), delim);
     }
 
     appendStringInfoChar(&state->accum_buf, NEWLINE);
@@ -119,12 +126,12 @@ Datum csv_agg_transfn(PG_FUNCTION_ARGS) {
     if (att->attisdropped) // pg always keeps dropped columns, guard against this
       continue;
 
-    if (i > 0) appendStringInfoChar(&state->accum_buf, DELIMITER);
+    if (i > 0) appendStringInfoChar(&state->accum_buf, delim);
 
     if (nulls[i]) continue; // empty field for NULL
 
     char *cstr = datum_to_cstring(datums[i], att->atttypid);
-    csv_append_field(&state->accum_buf, cstr, strlen(cstr));
+    csv_append_field(&state->accum_buf, cstr, strlen(cstr), delim);
   }
 
   PG_RETURN_POINTER(state);

src/pg_csv.c

@@ -41,10 +41,10 @@
 #include <utils/json.h>
 #include <utils/jsonb.h>
 #include <utils/lsyscache.h>
-#include <utils/typcache.h>
 #include <utils/memutils.h>
 #include <utils/regproc.h>
 #include <utils/snapmgr.h>
+#include <utils/typcache.h>
 #include <utils/varlena.h>
 
 #pragma GCC diagnostic pop

src/pg_prelude.h

@@ -0,0 +1,69 @@
+-- semicolon delimiter
+SELECT csv_agg(x, ';') AS body
+FROM   projects x;
+             body              
+-------------------------------
+ id;name;client_id            +
+ 1;Windows 7;1                +
+ 2;has,comma;1                +
+ ;;                           +
+ 4;OSX;2                      +
+ ;"has""quote";               +
+ 5;"has,comma and ""quote""";7+
+ 6;"has                       +
+  LF";7                       +
+ 7;"has \r CR";8              +
+ 8;"has \r                    +
+  CRLF""";8
+(1 row)
+
+-- pipe delimiter
+SELECT csv_agg(x, '|') AS body
+FROM   projects x;
+             body              
+-------------------------------
+ id|name|client_id            +
+ 1|Windows 7|1                +
+ 2|has,comma|1                +
+ ||                           +
+ 4|OSX|2                      +
+ |"has""quote"|               +
+ 5|"has,comma and ""quote"""|7+
+ 6|"has                       +
+  LF"|7                       +
+ 7|"has \r CR"|8              +
+ 8|"has \r                    +
+  CRLF"""|8
+(1 row)
+
+-- tab delimiter
+SELECT csv_agg(x, E'\t') AS body
+FROM   projects x;
+                   body                    
+-------------------------------------------
+ id      name    client_id                +
+ 1       Windows 7       1                +
+ 2       has,comma       1                +
+                                          +
+ 4       OSX     2                        +
+         "has""quote"                     +
+ 5       "has,comma and ""quote"""       7+
+ 6       "has                             +
+  LF"    7                                +
+ 7       "has \r CR"     8                +
+ 8       "has \r                          +
+  CRLF"""        8
+(1 row)
+
+-- newline is forbidden as delimiter
+SELECT csv_agg(x, E'\n') AS body
+FROM   projects x;
+ERROR:  delimiter cannot be newline, carriage return or double quote
+-- double quote is forbidden as delimiter
+SELECT csv_agg(x, '"') AS body
+FROM   projects x;
+ERROR:  delimiter cannot be newline, carriage return or double quote
+-- carriage return is forbidden as delimiter
+SELECT csv_agg(x, E'\r') AS body
+FROM   projects x;
+ERROR:  delimiter cannot be newline, carriage return or double quote

test/expected/delimiters.out

@@ -0,0 +1,23 @@
+-- semicolon delimiter
+SELECT csv_agg(x, ';') AS body
+FROM   projects x;
+
+-- pipe delimiter
+SELECT csv_agg(x, '|') AS body
+FROM   projects x;
+
+-- tab delimiter
+SELECT csv_agg(x, E'\t') AS body
+FROM   projects x;
+
+-- newline is forbidden as delimiter
+SELECT csv_agg(x, E'\n') AS body
+FROM   projects x;
+
+-- double quote is forbidden as delimiter
+SELECT csv_agg(x, '"') AS body
+FROM   projects x;
+
+-- carriage return is forbidden as delimiter
+SELECT csv_agg(x, E'\r') AS body
+FROM   projects x;