pg: Add a few result fetching methods

I'm not sure if these are free from memory leaks, need to find a way to
test for that.

c/libpq.h

@@ -47,9 +47,13 @@ typedef enum { PQSHOW_CONTEXT_NEVER, PQSHOW_CONTEXT_ERRORS, PQSHOW_CONTEXT_ALWAY
     X(PQfname, char *, const PGresult *, int) \
     X(PQfreemem, void, void *) \
     X(PQftype, Oid, const PGresult *, int) \
+    X(PQgetisnull, int, const PGresult *, int, int) \
+    X(PQgetlength, int, const PGresult *, int, int) \
+    X(PQgetvalue, char *, const PGresult *, int, int) \
     X(PQlibVersion, int, void) \
     X(PQnfields, int, const PGresult *) \
     X(PQnparams, int, const PGresult *) \
+    X(PQntuples, int, const PGresult *) \
     X(PQparamtype, Oid, const PGresult *, int) \
     X(PQprepare, PGresult *, PGconn *, const char *, const char *, int, const Oid *) \
     X(PQresStatus, char *, ExecStatusType) \

c/pgconn.c

@@ -112,6 +112,13 @@ static SV *fupg_exec(pTHX_ fupg_conn *c, const char *sql) {
     return ret;
 }
 
+/* Read a Perl value from a PGresult.
+ * Currently assumes text format and just creates a PV. */
+static SV *fupg_val(pTHX_ const PGresult *r, int row, int col) {
+    if (PQgetisnull(r, row, col)) return newSV(0);
+    return newSVpvn_utf8(PQgetvalue(r, row, col), PQgetlength(r, row, col), 1);
+}
+
 typedef struct {
     /* Set in $conn->q() */
     SV *self;
@@ -199,6 +206,21 @@ static SV *fupg_st_columns(pTHX_ fupg_st *st) {
     return sv_2mortal(newRV_noinc((SV *)av));
 }
 
+static void fupg_st_check_dupcols(pTHX_ PGresult *r) {
+    HV *hv = newHV();
+    int i, nfields = PQnfields(r);
+    for (i=0; i<nfields; i++) {
+        const char *key = PQfname(r, i);
+        int len = -strlen(key);
+        if (hv_exists(hv, key, len)) {
+            SvREFCNT_dec((SV *)hv);
+            croak("Query returns multiple columns with the same name ('%s')", key);
+        }
+        hv_store(hv, key, len, &PL_sv_yes, 0);
+    }
+    SvREFCNT_dec((SV *)hv);
+}
+
 static void fupg_st_execute(pTHX_ fupg_st *st) {
     /* Disallow fetching the results more than once. I don't see a reason why
      * someone would need that and disallowing it leaves room for fetching the
@@ -240,6 +262,59 @@ static SV *fupg_st_exec(pTHX_ fupg_st *st) {
     return fupg_exec_result(st->result);
 }
 
+static SV *fupg_st_val(pTHX_ fupg_st *st) {
+    fupg_st_prepare(aTHX_ st);
+    if (PQnfields(st->describe) > 1) croak("Invalid use of $st->val() on query returning more than one column");
+    if (PQnfields(st->describe) == 0) croak("Invalid use of $st->val() on query returning no data");
+    fupg_st_execute(aTHX_ st);
+    if (PQntuples(st->result) > 1) croak("Invalid use of $st->val() on query returning more than one row");
+    SV *sv = PQntuples(st->result) == 0 ? newSV(0) : fupg_val(aTHX_ st->result, 0, 0);
+    return sv_2mortal(sv);
+}
+
+static I32 fupg_st_rowl(pTHX_ fupg_st *st, I32 ax) {
+    dSP;
+    fupg_st_execute(aTHX_ st);
+    if (PQntuples(st->result) == 0) croak("Invalid use of $st->rowl() on query returning zero rows");
+    if (PQntuples(st->result) > 1) croak("Invalid use of $st->rowl() on query returning more than one row");
+    if (GIMME_V != G_LIST) {
+        ST(0) = sv_2mortal(newSViv(PQnfields(st->result)));
+        return 1;
+    }
+    int i, nfields = PQnfields(st->result);
+    (void)POPs;
+    EXTEND(SP, nfields);
+    for (i=0; i<nfields; i++) mPUSHs(fupg_val(aTHX_ st->result, 0, i));
+    return nfields;
+}
+
+static SV *fupg_st_rowa(pTHX_ fupg_st *st) {
+    fupg_st_execute(aTHX_ st);
+    if (PQntuples(st->result) == 0) croak("Invalid use of $st->rowl() on query returning zero rows");
+    if (PQntuples(st->result) > 1) croak("Invalid use of $st->rowl() on query returning more than one row");
+    int i, nfields = PQnfields(st->result);
+    AV *av = newAV_alloc_x(nfields);
+    SV *sv = sv_2mortal(newRV_noinc((SV *)av));
+    for (i=0; i<nfields; i++) av_push_simple(av, fupg_val(aTHX_ st->result, 0, i));
+    return sv;
+}
+
+static SV *fupg_st_rowh(pTHX_ fupg_st *st) {
+    fupg_st_prepare(aTHX_ st);
+    fupg_st_check_dupcols(aTHX_ st->describe);
+    fupg_st_execute(aTHX_ st);
+    if (PQntuples(st->result) == 0) croak("Invalid use of $st->rowh() on query returning zero rows");
+    if (PQntuples(st->result) > 1) croak("Invalid use of $st->rowh() on query returning more than one row");
+    int i, nfields = PQnfields(st->result);
+    HV *hv = newHV();
+    SV *sv = sv_2mortal(newRV_noinc((SV *)hv));
+    for (i=0; i<nfields; i++) {
+        const char *key = PQfname(st->result, i);
+        hv_store(hv, key, -strlen(key), fupg_val(aTHX_ st->result, 0, i), 0);
+    }
+    return sv;
+}
+
 static void fupg_st_destroy(fupg_st *st) {
     int i;
     /* Ignore failure, this is just a best-effort attempt to free up resources on the backend */
@@ -255,3 +330,9 @@ static void fupg_st_destroy(fupg_st *st) {
     SvREFCNT_dec(st->conn->self);
     safefree(st);
 }
+
+
+/* TODO: $st->alla, allh, flat, kvv, kva, kvh */
+/* TODO: Prepared statement caching */
+/* TODO: Transactions */
+/* TODO: Binary format fetching & type handling */