Add a converter that extracts a parameter from string of delimited
key/value pairs.

Fixes: #1697
---
 doc/configuration.txt         | 26 ++++++++++++
 reg-tests/converter/param.vtc | 80 +++++++++++++++++++++++++++++++++++
 src/sample.c                  | 64 ++++++++++++++++++++++++++++
 3 files changed, 170 insertions(+)
 create mode 100644 reg-tests/converter/param.vtc

diff --git a/doc/configuration.txt b/doc/configuration.txt
index c45f0b4b68..0cc2bdee3b 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -17702,6 +17702,32 @@ or(<value>)
   This prefix is followed by a name. The separator is a '.'. The name may only
   contain characters 'a-z', 'A-Z', '0-9', '.' and '_'.
 
+param(<name>,[<delim>])
+  This extracts the first occurrence of the parameter <name> in the input 
string
+  where parameters are delimited by <delim>, which defaults to "&", and the 
name
+  and value of the parameter are separated by a "=". If there is no "=" and
+  value before the end of the parameter segment, it is treated as equivalent to
+  a value of an empty string.
+
+  This can be useful for extracting parameters from a query string, or possibly
+  a x-www-form-urlencoded body. In particular, `query,param(<name>)` can be 
used
+  as an alternative to `urlp(<name>)` which only uses "&" as a delimiter,
+  whereas "urlp" also uses "?" and ";".
+
+  Note that this converter doesn't do anything special with url encoded
+  characters. If you want to decode the value, you can use the url_dec 
converter
+  on the output. If the name of the parameter in the input might contain 
encoded
+  characters, you'll probably want do normalize the input before calling
+  "param". This can be done using "http-request normalize-uri", in particular
+  the percent-decode-unreserved and percent-to-uppercase options.
+
+  Example :
+      str(a=b&c=d&a=r),param(a)   # b
+      str(a&b=c),param(a)         # ""
+      str(a=&b&c=a),param(b)      # ""
+      str(a=1;b=2;c=4),param(b,;) # 2
+      query,param(redirect_uri),urldec()
+
 port_only
   Converts a string which contains a Host header value into an integer by
   returning its port.
diff --git a/reg-tests/converter/param.vtc b/reg-tests/converter/param.vtc
new file mode 100644
index 0000000000..1633603823
--- /dev/null
+++ b/reg-tests/converter/param.vtc
@@ -0,0 +1,80 @@
+varnishtest "param converter Test"
+
+feature ignore_unknown_macro
+
+server s1 {
+       rxreq
+       txresp -hdr "Connection: close"
+} -repeat 10 -start
+
+haproxy h1 -conf {
+       defaults
+       mode http
+       timeout connect "${HAPROXY_TEST_TIMEOUT-5s}"
+       timeout client  "${HAPROXY_TEST_TIMEOUT-5s}"
+       timeout server  "${HAPROXY_TEST_TIMEOUT-5s}"
+
+       frontend fe
+       bind "fd@${fe}"
+
+       ### requests
+       http-request set-var(txn.query) query
+       http-response set-header Found %[var(txn.query),param(test)] if { 
var(txn.query),param(test) -m found }
+
+       default_backend be
+
+       backend be
+       server s1 ${s1_addr}:${s1_port}
+} -start
+
+client c1 -connect ${h1_fe_sock} {
+       txreq -url "/foo/?test=1&b=4&d"
+       rxresp
+       expect resp.status == 200
+       expect resp.http.found == "1"
+
+       txreq -url "/?a=1&b=4&test=34"
+       rxresp
+       expect resp.status == 200
+       expect resp.http.found == "34"
+
+       txreq -url "/?test=bar"
+       rxresp
+       expect resp.status == 200
+       expect resp.http.found == "bar"
+
+       txreq -url "/?a=b&c=d"
+       rxresp
+       expect resp.status == 200
+       expect resp.http.found == "<undef>"
+
+       txreq -url "/?a=b&test=t&c=d"
+       rxresp
+       expect resp.status == 200
+       expect resp.http.found == "t"
+
+       txreq -url "/?a=b&test&c=d"
+       rxresp
+       expect resp.status == 200
+       expect resp.http.found == ""
+
+       txreq -url "/?test="
+       rxresp
+       expect resp.status == 200
+       expect resp.http.found == ""
+
+    txreq -url "/?a=b&test"
+    rxresp
+    expect resp.status == 200
+    expect resp.http.found == ""
+
+    txreq -url "/?testing=123"
+    rxresp
+    expect resp.status == 200
+    expect resp.http.found == "<undef>"
+
+    txreq -url "/?testing=123&test=4"
+    rxresp
+    expect resp.status == 200
+    expect resp.http.found == "4"
+} -run
diff --git a/src/sample.c b/src/sample.c
index 62a372b81c..7a612fc033 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -2607,6 +2607,69 @@ static int sample_conv_word(const struct arg *arg_p, 
struct sample *smp, void *p
        return 1;
 }
 
+static int sample_conv_param_check(struct arg *arg, struct sample_conv *conv,
+                                   const char *file, int line, char **err)
+{
+       if (arg[1].type == ARGT_STR && arg[1].data.str.data != 1) {
+               memprintf(err, "Delimiter must be exactly 1 character.");
+               return 0;
+       }
+
+       return 1;
+}
+
+static int sample_conv_param(const struct arg *arg_p, struct sample *smp, void 
*private)
+{
+       char *pos, *end, *pend, *equal;
+       char delim = '&';
+       const char *name = arg_p[0].data.str.area;
+       size_t name_l = arg_p[0].data.str.data;
+
+       if (arg_p[1].type == ARGT_STR)
+               delim = *arg_p[1].data.str.area;
+
+       pos = smp->data.u.str.area;
+       end = pos + smp->data.u.str.data;
+       while (pos < end) {
+               equal = pos + name_l;
+               /* Parameter not found */
+               if (equal > end)
+                       break;
+
+               if (equal == end || *equal == delim) {
+                       if (memcmp(pos, name, name_l) == 0) {
+                               /* input contains parameter, but no value is 
supplied */
+                               smp->data.u.str.data = 0;
+                               return 1;
+                       }
+                       pos = equal + 1;
+                       continue;
+               }
+
+               if (*equal == '=' && memcmp(pos, name, name_l) == 0) {
+                       pos = equal + 1;
+                       pend = memchr(pos, delim, end - pos);
+                       if (pend == NULL)
+                               pend = end;
+
+                       if (smp->data.u.str.size)
+                               smp->data.u.str.size -= pos - 
smp->data.u.str.area;
+                       smp->data.u.str.area = pos;
+                       smp->data.u.str.data = pend - pos;
+                       return 1;
+               }
+               /* find the next delimiter and set position to character after 
that */
+               pos = memchr(pos, delim, end - pos);
+               if (pos == NULL)
+                       pos = end;
+               else
+                       pos++;
+       }
+       /* Parameter not found */
+       smp->data.u.str.data = 0;
+       return 0;
+}
+
 static int sample_conv_regsub_check(struct arg *args, struct sample_conv *conv,
                                     const char *file, int line, char **err)
 {
@@ -4399,6 +4462,7 @@ static struct sample_conv_kw_list sample_conv_kws = {ILH, 
{
        { "bytes",   sample_conv_bytes,        ARG2(1,SINT,SINT),     NULL,     
                SMP_T_BIN,  SMP_T_BIN  },
        { "field",   sample_conv_field,        ARG3(2,SINT,STR,SINT), 
sample_conv_field_check,  SMP_T_STR,  SMP_T_STR  },
        { "word",    sample_conv_word,         ARG3(2,SINT,STR,SINT), 
sample_conv_field_check,  SMP_T_STR,  SMP_T_STR  },
+       { "param",   sample_conv_param,        ARG2(1,STR,STR),       
sample_conv_param_check,  SMP_T_STR,  SMP_T_STR  },
        { "regsub",  sample_conv_regsub,       ARG3(2,REG,STR,STR),   
sample_conv_regsub_check, SMP_T_STR,  SMP_T_STR  },
        { "sha1",    sample_conv_sha1,         0,                     NULL,     
                SMP_T_BIN,  SMP_T_BIN  },
        { "strcmp",  sample_conv_strcmp,       ARG1(1,STR),           
smp_check_strcmp,         SMP_T_STR,  SMP_T_SINT },
-- 
2.38.1


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