[PATCH] Add support for postgres:// URIs to PGDATABASE environment variable

The PGDATABASE is documented as behaving the same as the dbname connection
parameter but they differ in the support for postgres:// URIs: the
PGDATABASE will never be expanded even thought expand_dbname is set:

    $ psql postgres://localhost/test -c 'select 1' >/dev/null  # Works
    $ PGDATABASE=postgres://localhost/test psql -c 'select 1' >/dev/null  # Doesn't work
    psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: FATAL:  database
"postgres://localhost/test"does not exist
 

In the second command the postgres://localhost/test string has not been
interpreted and the connection fails.

In order to make PGDATABASE and dbname behave the same this patch adds
URIs support to the environment variable. This makes it convenient for
users to pass a single connection string when environment variables are
used.

When both PGDATABASE and dbname are a connection string, the values of
dbname will override the ones of PGDATABASE, e.g.

    $ PGDATABASE=postgres://localhost/test?sslmode=require psql postgres://host/db

is equivalent to

    $ psql postgres://host/db?sslmode=require

I did not write tests for this patch as I am not sure where to put them
since libpq_uri_regress uses PQconninfoParse() that does not read the
environment variables.
---
 src/interfaces/libpq/fe-connect.c | 52 +++++++++++++++++++++++++++----
 1 file changed, 46 insertions(+), 6 deletions(-)

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index fcd3d0d9a3..64d6685ad8 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -412,7 +412,7 @@ static PQconninfoOption *conninfo_array_parse(const char *const *keywords,
                                               const char *const *values, PQExpBuffer errorMessage,
                                               bool use_defaults, int expand_dbname);
 static bool conninfo_add_defaults(PQconninfoOption *options,
-                                  PQExpBuffer errorMessage);
+                                  PQExpBuffer errorMessage, int expand_dbname);
 static PQconninfoOption *conninfo_uri_parse(const char *uri,
                                             PQExpBuffer errorMessage, bool use_defaults);
 static bool conninfo_uri_parse_options(PQconninfoOption *options,
@@ -1791,7 +1791,7 @@ PQconndefaults(void)
     if (connOptions != NULL)
     {
         /* pass NULL errorBuf to ignore errors */
-        if (!conninfo_add_defaults(connOptions, NULL))
+        if (!conninfo_add_defaults(connOptions, NULL, false))
         {
             PQconninfoFree(connOptions);
             connOptions = NULL;
@@ -6084,7 +6084,7 @@ conninfo_parse(const char *conninfo, PQExpBuffer errorMessage,
      */
     if (use_defaults)
     {
-        if (!conninfo_add_defaults(options, errorMessage))
+        if (!conninfo_add_defaults(options, errorMessage, false))
         {
             PQconninfoFree(options);
             return NULL;
@@ -6250,7 +6250,7 @@ conninfo_array_parse(const char *const *keywords, const char *const *values,
      */
     if (use_defaults)
     {
-        if (!conninfo_add_defaults(options, errorMessage))
+        if (!conninfo_add_defaults(options, errorMessage, expand_dbname))
         {
             PQconninfoFree(options);
             return NULL;
@@ -6272,7 +6272,7 @@ conninfo_array_parse(const char *const *keywords, const char *const *values,
  * NULL.
  */
 static bool
-conninfo_add_defaults(PQconninfoOption *options, PQExpBuffer errorMessage)
+conninfo_add_defaults(PQconninfoOption *options, PQExpBuffer errorMessage, int expand_dbname)
 {
     PQconninfoOption *option;
     PQconninfoOption *sslmode_default = NULL,
@@ -6296,6 +6296,46 @@ conninfo_add_defaults(PQconninfoOption *options, PQExpBuffer errorMessage)
         if (strcmp(option->keyword, "sslrootcert") == 0)
             sslrootcert = option;    /* save for later */
 
+        if (expand_dbname && strcmp(option->keyword, "dbname") == 0)
+        {
+            if ((tmp = getenv(option->envvar)) != NULL && recognized_connection_string(tmp))
+            {
+                PQconninfoOption *str_option,
+                                 *dbname_options = parse_connection_string(tmp, errorMessage, false);
+
+                if (dbname_options == NULL)
+                    return false;
+
+                for (str_option = dbname_options; str_option->keyword != NULL; str_option++)
+                {
+                    if (str_option->val != NULL)
+                    {
+                        int            k;
+
+                        for (k = 0; options[k].keyword; k++)
+                        {
+                            if (strcmp(options[k].keyword, str_option->keyword) == 0)
+                            {
+                                if (options[k].val != NULL)
+                                    continue;
+
+                                options[k].val = strdup(str_option->val);
+                                if (!options[k].val)
+                                {
+                                    libpq_append_error(errorMessage, "out of memory");
+                                    PQconninfoFree(dbname_options);
+                                    return false;
+                                }
+                                break;
+                            }
+                        }
+                    }
+                }
+                PQconninfoFree(dbname_options);
+                continue;
+            }
+        }
+
         if (option->val != NULL)
             continue;            /* Value was in conninfo or service */
 
@@ -6428,7 +6468,7 @@ conninfo_uri_parse(const char *uri, PQExpBuffer errorMessage,
      */
     if (use_defaults)
     {
-        if (!conninfo_add_defaults(options, errorMessage))
+        if (!conninfo_add_defaults(options, errorMessage, true))
         {
             PQconninfoFree(options);
             return NULL;
-- 
2.39.2 (Apple Git-143)