Fix COPY FROM for null marker strings that correspond to invalid encoding.

The COPY documentation says "COPY FROM matches the input against the null
string before removing backslashes".  It is therefore reasonable to presume
that null markers like E'\\0' will work ... and they did, until someone put
the tests in the wrong order during microoptimization-driven rewrites.
Since then, we've been failing if the null marker is something that would
de-escape to an invalidly-encoded string.  Since null markers generally
need to be something that can't appear in the data, this represents a
nontrivial loss of functionality; surprising nobody noticed it earlier.

Per report from Jeff Davis.  Backpatch to 8.4 where this got broken.

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index a6e1d354360baaecd56e795fdc903f0aeda690e6..f1ae42fb388a81d0d18cdb844ad4d171aeac12f5 100644 (file)
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -2767,7 +2767,17 @@ CopyReadAttributesText(CopyState cstate, int maxfields, char **fieldvals)
        start_ptr = cur_ptr;
        fieldvals[fieldno] = output_ptr;
 
-       /* Scan data for field */
+       /*
+        * Scan data for field.
+        *
+        * Note that in this loop, we are scanning to locate the end of field
+        * and also speculatively performing de-escaping.  Once we find the
+        * end-of-field, we can match the raw field contents against the null
+        * marker string.  Only after that comparison fails do we know that
+        * de-escaping is actually the right thing to do; therefore we *must
+        * not* throw any syntax errors before we've done the null-marker
+        * check.
+        */
        for (;;)
        {
            char        c;
@@ -2880,26 +2890,29 @@ CopyReadAttributesText(CopyState cstate, int maxfields, char **fieldvals)
            *output_ptr++ = c;
        }
 
-       /* Terminate attribute value in output area */
-       *output_ptr++ = '\0';
-
-       /*
-        * If we de-escaped a non-7-bit-ASCII char, make sure we still have
-        * valid data for the db encoding. Avoid calling strlen here for the
-        * sake of efficiency.
-        */
-       if (saw_non_ascii)
-       {
-           char       *fld = fieldvals[fieldno];
-
-           pg_verifymbstr(fld, output_ptr - (fld + 1), false);
-       }
-
        /* Check whether raw input matched null marker */
        input_len = end_ptr - start_ptr;
        if (input_len == cstate->null_print_len &&
            strncmp(start_ptr, cstate->null_print, input_len) == 0)
            fieldvals[fieldno] = NULL;
+       else
+       {
+           /*
+            * At this point we know the field is supposed to contain data.
+            *
+            * If we de-escaped any non-7-bit-ASCII chars, make sure the
+            * resulting string is valid data for the db encoding.
+            */
+           if (saw_non_ascii)
+           {
+               char       *fld = fieldvals[fieldno];
+
+               pg_verifymbstr(fld, output_ptr - fld, false);
+           }
+       }
+
+       /* Terminate attribute value in output area */
+       *output_ptr++ = '\0';
 
        fieldno++;
        /* Done if we hit EOL instead of a delim */

diff --git a/src/test/regress/expected/copy2.out b/src/test/regress/expected/copy2.out
index 15cbe02977008dcf3d7f1f482bdd65b30793f551..fc2c54dc36fb0f94d6a6e76722213986881b07a2 100644 (file)
--- a/src/test/regress/expected/copy2.out
+++ b/src/test/regress/expected/copy2.out
@@ -239,6 +239,22 @@ a\.
 \.b
 c\.d
 "\."
+-- test handling of nonstandard null marker that violates escaping rules
+CREATE TEMP TABLE testnull(a int, b text);
+INSERT INTO testnull VALUES (1, E'\\0'), (NULL, NULL);
+COPY testnull TO stdout WITH NULL AS E'\\0';
+1  \\0
+\0 \0
+COPY testnull FROM stdin WITH NULL AS E'\\0';
+SELECT * FROM testnull;
+ a  | b  
+----+----
+  1 | \0
+    | 
+ 42 | \0
+    | 
+(4 rows)
+
 DROP TABLE x, y;
 DROP FUNCTION fn_x_before();
 DROP FUNCTION fn_x_after();

diff --git a/src/test/regress/sql/copy2.sql b/src/test/regress/sql/copy2.sql
index c2e8b037e74be329c0829e4c6c25c4a4106e23c7..398f2ad798003b308738db73b11ccebb6225adbc 100644 (file)
--- a/src/test/regress/sql/copy2.sql
+++ b/src/test/regress/sql/copy2.sql
@@ -164,6 +164,21 @@ c\.d
 
 COPY testeoc TO stdout CSV;
 
+-- test handling of nonstandard null marker that violates escaping rules
+
+CREATE TEMP TABLE testnull(a int, b text);
+INSERT INTO testnull VALUES (1, E'\\0'), (NULL, NULL);
+
+COPY testnull TO stdout WITH NULL AS E'\\0';
+
+COPY testnull FROM stdin WITH NULL AS E'\\0';
+42 \\0
+\0 \0
+\.
+
+SELECT * FROM testnull;
+
+
 DROP TABLE x, y;
 DROP FUNCTION fn_x_before();
 DROP FUNCTION fn_x_after();