From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Tue, 17 May 2016 17:05:37 +0000 (+0100)
Subject: Merge branch 'mdw+fixes'
X-Git-Url: https://git.distorted.org.uk/~mdw/userv-utils/commitdiff_plain/0324503152d6edb67572b45225745441913ae55e?hp=f34db0d4628fd5a077ac48a627b4491c5d933d62

Merge branch 'mdw+fixes'
---

diff --git a/www-cgi/README.custom-env-filter b/www-cgi/README.custom-env-filter
new file mode 100644
index 0000000..58ef39b
--- /dev/null
+++ b/www-cgi/README.custom-env-filter
@@ -0,0 +1,27 @@
+Allow customization of the environment filters.
+    
+Sites can configure ucgi's environment filters, and end users can
+configure ucgitarget's filters.
+
+By default, ucgi will look in /etc/userv/ucgi.env-filter, but if
+UCGI_ENV_FILTER is set in its environment, it will look there
+instead.  The filter may contain wildcards and so on.
+
+By default, ucgitarget looks in .userv/ucgitarget.env-filter, or
+/etc/userv/ucgitarget.env-filter, if the former doesn't exist; but if
+passed a `-e FILTER' option on its command line, it will look in the
+file FILTER instead.  This filter may /not/ contain wildcards.
+
+In both cases, if an explicitly named filter file can't be found then
+the program fails; if the default filter files can't be found then they
+fall back to built-in lists.
+
+The reason for the asymmetry in interfaces is: it's hard to pass
+command-line options to CGI scripts from webservers, but pretty easy to
+set environment variables; whereas it's hard to pass environment
+variables to a service program in a Userv configuration file, but easy
+to pass command-line arguments.
+
+
+The `?DEFAULTS' pattern can be specified to match the default set
+(which is different in `ucgi' and `ucgitarget').
diff --git a/www-cgi/ucgi.c b/www-cgi/ucgi.c
index 8d6fa0d..9433020 100644
--- a/www-cgi/ucgi.c
+++ b/www-cgi/ucgi.c
@@ -31,14 +31,58 @@
 
 #include "ucgi.h"
 
+static const char *const default_envok[] = {
+  "AUTH_TYPE",
+  "CONTENT_TYPE",
+  "CONTENT_LENGTH",
+  "DOCUMENT_ROOT",
+  "GATEWAY_INTERFACE",
+  "HTTP_*",
+  "HTTPS",
+  "PATH_INFO",
+  "PATH_TRANSLATED",
+  "QUERY_STRING",
+  "REDIRECT_*",
+  "REMOTE_*",
+  "REQUEST_METHOD",
+  "REQUEST_URI",
+  "SCRIPT_*",
+  "SERVER_*",
+  "SSL_*",
+  0
+};
+
+struct buildargs {
+  const char **v;
+  int n, max;
+};
+
+static void addarg(struct buildargs *args, const char *a) {
+  if (args->n > args->max) error("too many arguments", 500);
+  args->v[args->n++]= a;
+}
+
+static void add_userv_var(const char *fulln,
+			  const char *en, const char *ev, void *p) {
+  struct buildargs *args= p;
+  size_t l;
+  char *a;
+
+  l= strlen(ev);
+  if (l > MAX_ENVVAR_VALUE) error("environment variable too long", 500);
+  a= xmalloc(strlen(en)+l+6);
+  sprintf(a,"-DE_%s=%s",en,ev);
+  addarg(args, a);
+}
+
 int main(int argc, const char **argv) {
-  char *defarg, *username;
-  const char *slash2, *pathi, *ev, *en, *av;
-  const char *const *ep;
-  const char **arguments;
+  char *username;
+  const char *slash2, *pathi, *ev, *av;
+  const char *const *envok = 0;
   size_t usernamelen, l;
+  struct buildargs args;
   pid_t child, rchild;
-  int nargs, status;
+  int status;
 
   l= strlen(argv[0]);
   if (l>6 && !strcmp(argv[0]+l-6,"-debug")) debugmode= 1;
@@ -47,41 +91,54 @@ int main(int argc, const char **argv) {
     if (fputs("Content-Type: text/plain\n\n",stdout)==EOF || fflush(stdout))
       syserror("write stdout");
     if (dup2(1,2)<0) { perror("dup stdout to stderr"); exit(-1); }
+    D( printf(";;; UCGI\n"); )
   }
   
-  if (argc > MAX_ARGS) error("too many arguments");
+  if (argc > MAX_ARGS) error("too many arguments", 500);
+
+  ev= getenv("UCGI_ENV_FILTER");
+  if (ev)
+    envok= load_filters(LOADF_MUST, ev, LF_END);
+  else
+    envok= load_filters(0, "/etc/userv/ucgi.env-filter", LF_END);
 
   pathi= getenv("PATH_INFO");
-  if (!pathi) error("PATH_INFO not found");
-  if (pathi[0] != '/' || pathi[1] != '~') error("PATH_INFO must start with /~");
-  slash2= strchr(pathi+2,'/'); if (!slash2) error("PATH_INFO must have more than one /");
+  if (!pathi) error("PATH_INFO not found", 500);
+  D( if (debugmode) {
+       printf(";; find user name...\n"
+	      ";;   initial PATH_INFO = `%s'\n",
+	      pathi);
+  } )
+  if (pathi[0] != '/' || pathi[1] != '~')
+    error("PATH_INFO must start with /~", 400);
+  slash2= strchr(pathi+2,'/');
+  if (!slash2) error("PATH_INFO must have more than one /", 400);
   usernamelen= slash2-(pathi+2);
-  if (usernamelen > MAX_USERNAME_LEN) error("PATH_INFO username too long");
+  if (usernamelen > MAX_USERNAME_LEN) error("PATH_INFO username too long", 400);
   username= xmalloc(usernamelen+1);
   memcpy(username,pathi+2,usernamelen); username[usernamelen]= 0;
-  if (!isalpha(username[0])) error("username 1st character is not alphabetic");
+  D( if (debugmode)
+       printf(";;   user = `%s'; tail = `%s'\n", username, slash2); )
+  if (!isalpha(username[0]))
+    error("username 1st character is not alphabetic", 400);
   xsetenv("PATH_INFO",slash2,1);
+
+  args.n= 0; args.max= argc + MAX_ENVVARS + 10;
+  args.v= xmalloc(args.max * sizeof(*args.v));
   
-  arguments= xmalloc(sizeof(const char*)*(nenvok+argc+10));
-  nargs= 0;
-  
-  arguments[nargs++]= "userv";
-  if (debugmode) arguments[nargs++]= "-DDEBUG=1";
-  
-  for (ep= envok; (en= *ep); ep++) {
-    ev= getenv(en); if (!ev) continue;
-    l= strlen(ev); if (l > MAX_ENVVAR_VALUE) error("environment variable too long");
-    defarg= xmalloc(strlen(en)+l+6);
-    sprintf(defarg,"-DE_%s=%s",en,ev);
-    arguments[nargs++]= defarg;
-  }
+  addarg(&args, "userv");
+  if (debugmode) addarg(&args, "-DDEBUG=1");
 
-  arguments[nargs++]= username;
-  arguments[nargs++]= "www-cgi";
-  while ((av= (*++argv))) arguments[nargs++]= av;
-  arguments[nargs++]= 0;
+  filter_environment(FILTF_WILDCARD, "", envok, default_envok,
+		     add_userv_var, &args);
+
+  addarg(&args, username);
+  addarg(&args, "www-cgi");
+  while ((av= (*++argv))) addarg(&args, av);
+  addarg(&args, 0);
 
   if (debugmode) {
+    D( fflush(stdout); )
     child= fork(); if (child==-1) syserror("fork");
     if (child) {
       rchild= waitpid(child,&status,0);
@@ -91,7 +148,16 @@ int main(int argc, const char **argv) {
     }
   }
       
-  execvp("userv",(char*const*)arguments);
+  D( if (debugmode) {
+       int i;
+
+       printf(";; final command line...\n");
+       for (i = 0; args.v[i]; i++)
+	 printf(";;   %s\n", args.v[i]);
+       fflush(stdout);
+  } )
+
+  execvp("userv",(char*const*)args.v);
   syserror("exec userv");
   return -1;
 }
diff --git a/www-cgi/ucgi.h b/www-cgi/ucgi.h
index ed225fd..dd90b23 100644
--- a/www-cgi/ucgi.h
+++ b/www-cgi/ucgi.h
@@ -24,18 +24,37 @@
 
 #include <stdlib.h>
 
+#ifdef DEBUG
+#  define D(x) x
+#else
+#  define D(x)
+#endif
+
 #define MAX_ARGS 1024
 #define MAX_USERNAME_LEN 1024
 #define MAX_SCRIPTPATH_LEN 1024
+#define MAX_ENVVAR_NAME 128
 #define MAX_ENVVAR_VALUE (1024*1024)
+#define MAX_ENVVARS 256
 
 void syserror(const char *m);
-void error(const char *m);
+void error(const char *m, int st);
 void *xmalloc(size_t sz);
 void xsetenv(const char *en, const char *ev, int overwrite);
+void *xrealloc(void *ptr, size_t sz);
+
+const char **load_filters(unsigned flags, const char *first, ...);
+#define LOADF_MUST 1u
+#define LF_END ((const char *)0)
+
+void filter_environment(unsigned flags, const char *prefix_in,
+			const char *const *patv,
+			const char *const *defaults,
+			void (*foundone)(const char *fulln, const char *en,
+					 const char *ev, void *p),
+			void *p);
+#define FILTF_WILDCARD 1u
 
-extern const char *const envok[];
-extern const int nenvok;
 extern int debugmode;
 
 #endif
diff --git a/www-cgi/ucgicommon.c b/www-cgi/ucgicommon.c
index 090cc03..4d37187 100644
--- a/www-cgi/ucgicommon.c
+++ b/www-cgi/ucgicommon.c
@@ -19,59 +19,16 @@
  * along with userv-utils; if not, see http://www.gnu.org/licenses/.
  */
 
+#include <assert.h>
+#include <ctype.h>
+#include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
 #include <errno.h>
 
-#include "ucgi.h"
+#include <unistd.h>
 
-const char *const envok[]= {
-  "AUTH_TYPE",
-  "CONTENT_LENGTH",
-  "CONTENT_TYPE",
-  "DOCUMENT_ROOT",
-  "GATEWAY_INTERFACE",
-  "HTTP_ACCEPT",
-  "HTTP_ACCEPT_CHARSET",
-  "HTTP_ACCEPT_ENCODING",
-  "HTTP_ACCEPT_LANGUAGE",
-  "HTTP_CACHE_CONTROL",
-  "HTTP_CONNECTION",
-  "HTTP_CONTENT_ENCODING",
-  "HTTP_COOKIE",
-  "HTTP_DNT",
-  "HTTP_HOST",
-  "HTTP_KEEP_ALIVE",
-  "HTTP_NEGOTIATE",
-  "HTTP_PRAGMA",
-  "HTTP_REFERER",
-  "HTTP_USER_AGENT",
-  "HTTP_VIA",
-  "HTTP_X_FORWARDED_FOR",
-  "HTTPS",
-  "PATH_INFO",
-  "PATH_TRANSLATED",
-  "QUERY_STRING",
-  "REMOTE_ADDR",
-  "REMOTE_HOST",
-  "REMOTE_USER",
-  "REMOTE_IDENT",
-  "REQUEST_METHOD",
-  "REQUEST_URI",
-  "SCRIPT_FILENAME",
-  "SCRIPT_NAME",
-  "SCRIPT_URI",
-  "SCRIPT_URL",
-  "SERVER_ADDR",
-  "SERVER_ADMIN",
-  "SERVER_NAME",
-  "SERVER_PORT",
-  "SERVER_PROTOCOL",
-  "SERVER_SIGNATURE",
-  "SERVER_SOFTWARE",
-  0
-};
-const int nenvok= sizeof(envok)/sizeof(envok[0]);
+#include "ucgi.h"
 
 int debugmode= 0;
 
@@ -81,18 +38,20 @@ static void outerror(void) {
 }
 
 void syserror(const char *m) {
-  if (printf("Content-Type: text/plain\n\n"
+  if (printf("Content-Type: text/plain\n"
+	     "Status: 500\n\n"
 	     "ucgi: system call error:\n"
 	     "%s: %s\n",
 	     m,strerror(errno))==EOF || fflush(stdout)) outerror();
   exit(0);
 }
 
-void error(const char *m) {
-  if (printf("Content-Type: text/plain\n\n"
+void error(const char *m, int st) {
+  if (printf("Content-Type: text/plain\n"
+	     "Status: %d\n\n"
 	     "ucgi: error:\n"
 	     "%s\n",
-	     m)==EOF || fflush(stdout)) outerror();
+	     st, m)==EOF || fflush(stdout)) outerror();
   exit(0);
 }
 
@@ -104,6 +63,158 @@ void *xmalloc(size_t sz) {
   return r;
 }
 
+void *xrealloc(void *ptr, size_t sz) {
+  void *r;
+
+  r= realloc(ptr,sz);
+  if (!r) syserror("realloc failed");
+  return r;
+}
+
 void xsetenv(const char *en, const char *ev, int overwrite) {
   if (setenv(en,ev,overwrite)) syserror("setenv");
 }
+
+const char **load_filters(unsigned flags, const char *first, ...) {
+  va_list ap;
+  const char *name, *p, *q, **v;
+  char *pp;
+  size_t l, n, sz;
+  FILE *fp;
+  char buf[MAX_ENVVAR_NAME];
+
+  D( if (debugmode) printf(";; load_filters...\n"); )
+  va_start(ap, first);
+  for (name= first; name; name= va_arg(ap, const char *)) {
+    fp= fopen(name, "r"); if (fp) goto opened;
+    D( if (debugmode)
+	 printf(";;   file `%s': %s\n", name, strerror(errno)); )
+    if (errno != ENOENT) syserror("failed to open environment filters");
+  }
+  va_end(ap);
+  if (flags & LOADF_MUST) syserror("failed to open environment filters");
+  D( if (debugmode) printf(";;   using default filters\n"); )
+  return 0;
+
+opened:
+  va_end(ap);
+  D( if (debugmode) printf(";;   file `%s': OK\n", name); )
+
+  n= 0; sz= 128; v= xmalloc(sz * sizeof(*v));
+  for (;;) {
+    if (!fgets(buf, sizeof(buf), fp)) break;
+    l= strlen(buf);
+    if (buf[l - 1] == '\n') buf[--l]= 0;
+    if (l + 1 == sizeof(buf))
+      error("line too long in environment filter file", 500);
+    p= buf; q= p + l;
+    while (isspace((unsigned char)*p)) p++;
+    while (q > p && isspace((unsigned char)q[-1])) q--;
+    if (*p == '#' || p == q) continue;
+    l= q - p;
+    pp= xmalloc(l + 1);
+    memcpy(pp, p, l);
+    pp[l]= 0;
+    v[n++]= pp;
+    D( if (debugmode) printf(";;   filter: `%s'\n", pp); )
+    if (n >= sz) {
+      sz *= 2;
+      v= xrealloc(v, sz * sizeof(*v));
+    }
+  }
+  if (ferror(fp)) syserror("failed to read environment filters");
+  fclose(fp);
+  return v;
+}
+
+static int envvar_match(unsigned flags, const char *en,
+			const char *const *patv,
+			const char *const *defaults,
+			const char **ev) {
+  const char *const *patp;
+  const char *q, *pat;
+  int acceptp;
+  int rc;
+
+  if (!patv) { patv= defaults; defaults= 0; }
+  for (patp= patv; (pat= *patp); patp++) {
+    q= en;
+    acceptp= 1;
+    if (*pat == '!' && (flags & FILTF_WILDCARD)) { acceptp= 0; pat++; }
+    else if (*pat == '?') {
+      if (strcmp(pat + 1, "DEFAULTS") == 0) {
+	assert(defaults);
+	rc= envvar_match(flags, en, defaults, 0, ev);
+	if (rc) return rc;
+      } else
+	error("unknown pattern directive", 500);
+      continue;
+    }
+
+    for (;;) {
+      if (!*pat) {
+	if (*q != '=') {
+	  D( if (debugmode)
+	       printf(";;     mismatch `%s' (prefix)\n", *patp); )
+	  break;
+	}
+	D( if (debugmode) printf(";;     matched pattern `%s'\n", *patp); )
+	goto match;
+      } else if (*pat == '*' && (flags & FILTF_WILDCARD)) {
+	q = strchr(q, '=');
+	if (!q) {
+	  D( if (debugmode)
+	       printf(";;     mismatch `%s' (discard: no `=')\n", *patp); )
+	  return -1;
+	}
+	D( if (debugmode)
+	     printf(";;     wildcard match for `%s'\n", *patp); )
+	goto match;
+      } else {
+	if (*pat++ != *q++) {
+	  D( if (debugmode) printf(";;     mismatch `%s'\n", *patp); )
+	  break;
+	}
+      }
+    }
+  }
+  return 0;
+
+match:
+  if (!acceptp) return -1;
+  *ev= q + 1;
+  return +1;
+}
+
+void filter_environment(unsigned flags, const char *prefix_in,
+			const char *const *patv,
+			const char *const *defaults,
+			void (*foundone)(const char *fulln,
+					 const char *en, const char *ev,
+					 void *p),
+			void *p) {
+  char *const *ep;
+  const char *en, *ev;
+  char enbuf[MAX_ENVVAR_NAME];
+  size_t n, pn = strlen(prefix_in);
+
+  D( if (debugmode) printf(";; filter_environment...\n"); )
+  for (ep= environ; (en= *ep); ep++) {
+    D( if (debugmode) printf(";;   consider env-var `%s'\n", en); )
+    if (strncmp(en, prefix_in, pn) != 0 || !en[pn]) {
+      D( if (debugmode) printf(";;     doesn't match prefix\n"); )
+      continue;
+    }
+    if (envvar_match(flags, en + pn, patv, defaults, &ev) > 0) {
+      n= strcspn(en, "=");
+      if (n >= sizeof(enbuf))
+	error("environment variable name too long", 500);
+      memcpy(enbuf, en, n);
+      enbuf[n]= 0;
+      D( if (debugmode)
+	   printf(";;     full = `%s'; tail = `%s'; value = `%s'\n",
+		  enbuf, enbuf + pn, ev); )
+      foundone(enbuf, enbuf + pn, ev, p);
+    }
+  }
+}
diff --git a/www-cgi/ucgitarget.c b/www-cgi/ucgitarget.c
index 7a4e8bc..a24867d 100644
--- a/www-cgi/ucgitarget.c
+++ b/www-cgi/ucgitarget.c
@@ -26,6 +26,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <ctype.h>
+#include <getopt.h>
 #include <unistd.h>
 #include <sys/types.h>
 #include <sys/wait.h>
@@ -33,71 +34,144 @@
 
 #include "ucgi.h"
 
-static void *xrealloc(void *ptr, size_t sz) {
-  void *r;
+static const char *const default_envok[]= {
+  "AUTH_TYPE",
+  "CONTENT_LENGTH",
+  "CONTENT_TYPE",
+  "DOCUMENT_ROOT",
+  "GATEWAY_INTERFACE",
+  "HTTP_ACCEPT",
+  "HTTP_ACCEPT_CHARSET",
+  "HTTP_ACCEPT_ENCODING",
+  "HTTP_ACCEPT_LANGUAGE",
+  "HTTP_CACHE_CONTROL",
+  "HTTP_CONNECTION",
+  "HTTP_CONTENT_ENCODING",
+  "HTTP_COOKIE",
+  "HTTP_DNT",
+  "HTTP_HOST",
+  "HTTP_KEEP_ALIVE",
+  "HTTP_NEGOTIATE",
+  "HTTP_PRAGMA",
+  "HTTP_REFERER",
+  "HTTP_USER_AGENT",
+  "HTTP_VIA",
+  "HTTP_X_FORWARDED_FOR",
+  "HTTPS",
+  "PATH_INFO",
+  "PATH_TRANSLATED",
+  "QUERY_STRING",
+  "REDIRECT_HANDLER",
+  "REDIRECT_SCRIPT_URI",
+  "REDIRECT_SCRIPT_URL",
+  "REDIRECT_STATUS",
+  "REDIRECT_URL",
+  "REMOTE_ADDR",
+  "REMOTE_HOST",
+  "REMOTE_USER",
+  "REMOTE_IDENT",
+  "REQUEST_METHOD",
+  "REQUEST_URI",
+  "SCRIPT_FILENAME",
+  "SCRIPT_NAME",
+  "SCRIPT_URI",
+  "SCRIPT_URL",
+  "SERVER_ADDR",
+  "SERVER_ADMIN",
+  "SERVER_NAME",
+  "SERVER_PORT",
+  "SERVER_PROTOCOL",
+  "SERVER_SIGNATURE",
+  "SERVER_SOFTWARE",
+  "SSL_CIPHER",
+  "SSL_CLIENT_S_DN",
+  "SSL_CLIENT_VERIFY",
+  "SSL_PROTOCOL",
+  0
+};
 
-  r= realloc(ptr,sz);
-  if (!r) syserror("realloc failed");
-  return r;
+static void setenvar(const char *fulln,
+		     const char *en, const char *ep, void *p) {
+  xsetenv(en, ep, 1);
+  unsetenv(fulln);
 }
 
-int main(int argc, const char **argv) {
-  char *uservarn, *scriptpath, *newvar;
-  const char *nextslash, *lastslash, *pathi, *ev, *ev2, *en, *scriptdir, *av;
-  const char *const *ep;
+int main(int argc, char **argv) {
+  char *scriptpath, *newvar;
+  const char *nextslash, *lastslash, *pathi, *ev, *ev2, *scriptdir, *av;
+  const char *const *envok;
   const char **arguments;
-  size_t scriptdirlen, scriptpathlen, l, uservarnl;
+  size_t scriptdirlen, scriptpathlen, l;
   struct stat stab;
-  int r, nargs;
+  int i, r, nargs;
+  const char *filters= 0;
 
   ev= getenv("USERV_U_DEBUG");
   if (ev && *ev) debugmode= 1;
   
-  if (argc > MAX_ARGS) error("too many arguments");
+  D( if (debugmode) printf(";;; UCGITARGET\n"); )
+  if (argc > MAX_ARGS) error("too many arguments", 500);
 
-  if (!*++argv) error("no script directory argument");
-  ev= getenv("HOME"); if (!ev) error("no HOME env. var");
+  for (;;) {
+    i= getopt(argc, argv, "+e:"); if (i < 0) break;
+    switch (i) {
+    case 'e': filters= optarg; break;
+    default: error("bad command line", 500); break;
+    }
+  }
+  argc -= optind; argv += optind;
+
+  if (!*argv) error("no script directory argument", 500);
+  ev= getenv("HOME"); if (!ev) error("no HOME env. var", 500);
   l= strlen(*argv)+strlen(ev);
   newvar= xmalloc(l+2);
   sprintf(newvar,"%s/%s",ev,*argv);
   scriptdir= newvar;
   scriptdirlen= strlen(scriptdir);
 
-  uservarn= 0;
-  uservarnl= 0;
-  for (ep= envok; (en= *ep); ep++) {
-    l= strlen(en)+11;
-    if (uservarnl<l) { uservarn= xrealloc(uservarn,l); uservarnl= l; }
-    sprintf(uservarn,"USERV_U_E_%s",en);
-    ev= getenv(uservarn); if (!ev) continue;
-    if (strlen(ev) > MAX_ENVVAR_VALUE) error("environment variable too long");
-    if (setenv(en,ev,1)) syserror("setenv");
-    unsetenv(uservarn);
+  if (filters)
+    envok= load_filters(LOADF_MUST, filters, LF_END);
+  else {
+    envok= load_filters(0,
+			".userv/ucgitarget.env-filter",
+			"/etc/userv/ucgitarget.env-filter",
+			LF_END);
   }
 
+  filter_environment(0, "USERV_U_E_", envok, default_envok, setenvar, 0);
+
   scriptpath= 0;
   pathi= getenv("PATH_INFO");
-  if (!pathi) error("PATH_INFO not found");
+  if (!pathi) error("PATH_INFO not found", 500);
   lastslash= pathi;
+  D( if (debugmode) {
+       printf(";; find script name...\n"
+	      ";;   PATH_INFO = `%s'\n",
+	      pathi);
+  } )
   for (;;) {
-    if (*lastslash != '/') error("PATH_INFO expected slash not found");
-    if (lastslash[1]=='.' || lastslash[1]=='#' || !lastslash[1]) error("bad char begin");
+    if (*lastslash != '/') error("PATH_INFO expected slash not found", 400);
+    if (lastslash[1]=='.' || lastslash[1]=='#' || !lastslash[1])
+      error("bad char begin", 400);
     nextslash= strchr(lastslash+1,'/');
     if (!nextslash) nextslash= lastslash+1+strlen(lastslash+1);
-    if (!nextslash) error("insufficient elements in PATH_INFO");
-    if (nextslash==lastslash+1) error("empty component in PATH_INFO");
-    if (nextslash-pathi > MAX_SCRIPTPATH_LEN) error("PATH_INFO script path too long");
+    if (!nextslash) error("insufficient elements in PATH_INFO", 400);
+    if (nextslash==lastslash+1) error("empty component in PATH_INFO", 400);
+    if (nextslash-pathi > MAX_SCRIPTPATH_LEN)
+      error("PATH_INFO script path too long", 400);
     scriptpathlen= scriptdirlen+(nextslash-pathi);
     scriptpath= xrealloc(scriptpath,scriptpathlen+1);
     strcpy(scriptpath,scriptdir);
     memcpy(scriptpath+scriptdirlen,pathi,nextslash-pathi);
     scriptpath[scriptpathlen]= 0;
-    if (scriptpath[scriptpathlen-1]=='~') error("bad char end");
+    if (scriptpath[scriptpathlen-1]=='~') error("bad char end", 400);
+    D( if (debugmode) printf(";;   try `%s'\n", scriptpath); )
     r= stat(scriptpath,&stab); if (r) syserror("stat script");
     if (S_ISREG(stab.st_mode)) break;
-    if (!S_ISDIR(stab.st_mode)) syserror("script not directory or file");
+    if (!S_ISDIR(stab.st_mode)) error("script not directory or file", 500);
     lastslash= nextslash;
   }
+  D( if (debugmode) printf(";;   found script: tail = `%s'\n", nextslash); )
   if (*nextslash) xsetenv("PATH_INFO",nextslash,1);
   else unsetenv("PATH_INFO");
 
@@ -109,7 +183,7 @@ int main(int argc, const char **argv) {
 
   ev= getenv("SCRIPT_NAME");
   if (ev) {
-    ev2= getenv("USER"); if (!ev2) error("no USER variable");
+    ev2= getenv("USER"); if (!ev2) error("no USER variable", 500);
     newvar= xmalloc(strlen(ev)+2+strlen(ev2)+scriptpathlen-scriptdirlen+2);
     sprintf(newvar,"%s/~%s%s",ev,ev2,scriptpath+scriptdirlen);
     xsetenv("SCRIPT_NAME",newvar,1);
@@ -122,6 +196,19 @@ int main(int argc, const char **argv) {
   while ((av= (*++argv))) arguments[nargs++]= av;
   arguments[nargs++]= 0;
 
+  D( if (debugmode) {
+       int i;
+
+       printf(";; final environment...\n");
+       for (i = 0; environ[i]; i++)
+	 printf(";;   %s\n", environ[i]);
+
+       printf(";; final command line...\n");
+       for (i = 0; arguments[i]; i++)
+	 printf(";;   %s\n", arguments[i]);
+       fflush(stdout);
+  } )
+
   execvp(scriptpath,(char*const*)arguments);
   syserror("exec script");
   return -1;