setopt: add CURLOPT_DOH_URL

Closes #2668

1 files changed, 915 insertions, 0 deletions

diff --git a/lib/doh.c b/lib/doh.c
new file mode 100644
index 000000000..5d1cd3b78
--- /dev/null
+++ b/lib/doh.c
@@ -0,0 +1,915 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+
+#include "curl_setup.h"
+#include "urldata.h"
+#include "curl_addrinfo.h"
+#include "sendf.h"
+#include "multiif.h"
+#include "url.h"
+#include "share.h"
+#include "curl_base64.h"
+#include "connect.h"
+#include "doh.h"
+/* The last 3 #include files should be in this order */
+#include "curl_printf.h"
+#include "curl_memory.h"
+#include "memdebug.h"
+
+#define DNS_CLASS_IN 0x01
+#define DOH_MAX_RESPONSE_SIZE 3000 /* bytes */
+
+typedef enum {
+  DNS_TYPE_A = 1,
+  DNS_TYPE_NS = 2,
+  DNS_TYPE_CNAME = 5,
+  DNS_TYPE_AAAA = 28
+} DNStype;
+
+#define MAX_ADDR 24
+
+typedef enum {
+  DOH_OK,
+  DOH_DNS_BAD_LABEL,    /* 1 */
+  DOH_DNS_OUT_OF_RANGE, /* 2 */
+  DOH_DNS_LABEL_LOOP,   /* 3 */
+  DOH_TOO_SMALL_BUFFER, /* 4 */
+  DOH_OUT_OF_MEM,       /* 5 */
+  DOH_DNS_RDATA_LEN,    /* 6 */
+  DOH_DNS_MALFORMAT,    /* 7 */
+  DOH_DNS_BAD_RCODE,    /* 8 - no such name */
+  DOH_DNS_UNEXPECTED_TYPE,  /* 9 */
+  DOH_DNS_UNEXPECTED_CLASS, /* 10 */
+  DOH_NO_CONTENT,           /* 11 */
+  DOH_DNS_BAD_ID            /* 12 */
+} DOHcode;
+
+static const char * const errors[]={
+  "",
+  "Bad label",
+  "Out of range",
+  "Label loop",
+  "Too small",
+  "Out of memory",
+  "RDATA length",
+  "Malformat",
+  "Bad RCODE",
+  "Unexpected TYPE",
+  "Unexpected CLASS",
+  "No content",
+  "Bad ID"
+};
+
+static const char *doh_strerror(DOHcode code)
+{
+  if((code >= DOH_OK) && (code <= DOH_DNS_BAD_ID))
+    return errors[code];
+  return "bad error code";
+}
+
+static DOHcode doh_encode(const char *host,
+                          DNStype dnstype,
+                          unsigned char *dnsp, /* buffer */
+                          size_t len,  /* buffer size */
+                          size_t *olen) /* output length */
+{
+  size_t hostlen = strlen(host);
+  unsigned char *orig = dnsp;
+  const char *hostp = host;
+
+  if(len < (12 + hostlen + 4))
+    return DOH_TOO_SMALL_BUFFER;
+
+  *dnsp++ = 0; /* 16 bit id */
+  *dnsp++ = 0;
+  *dnsp++ = 0x01; /* |QR|   Opcode  |AA|TC|RD| Set the RD bit */
+  *dnsp++ = '\0'; /* |RA|   Z    |   RCODE   |                */
+  *dnsp++ = '\0';
+  *dnsp++ = 1;    /* QDCOUNT (number of entries in the question section) */
+  *dnsp++ = '\0';
+  *dnsp++ = '\0'; /* ANCOUNT */
+  *dnsp++ = '\0';
+  *dnsp++ = '\0'; /* NSCOUNT */
+  *dnsp++ = '\0';
+  *dnsp++ = '\0'; /* ARCOUNT */
+
+  /* store a QNAME */
+  do {
+    char *dot = strchr(hostp, '.');
+    size_t labellen;
+    bool found = false;
+    if(dot) {
+      found = true;
+      labellen = dot - hostp;
+    }
+    else
+      labellen = strlen(hostp);
+    if(labellen > 63)
+      /* too long label, error out */
+      return DOH_DNS_BAD_LABEL;
+    *dnsp++ = (unsigned char)labellen;
+    memcpy(dnsp, hostp, labellen);
+    dnsp += labellen;
+    hostp += labellen + 1;
+    if(!found) {
+      *dnsp++ = 0; /* terminating zero */
+      break;
+    }
+  } while(1);
+
+  *dnsp++ = '\0'; /* upper 8 bit TYPE */
+  *dnsp++ = (unsigned char)dnstype;
+  *dnsp++ = '\0'; /* upper 8 bit CLASS */
+  *dnsp++ = DNS_CLASS_IN; /* IN - "the Internet" */
+
+  *olen = dnsp - orig;
+  return DOH_OK;
+}
+
+static size_t
+doh_write_cb(void *contents, size_t size, size_t nmemb, void *userp)
+{
+  size_t realsize = size * nmemb;
+  struct dohresponse *mem = (struct dohresponse *)userp;
+
+  if((mem->size + realsize) > DOH_MAX_RESPONSE_SIZE)
+    /* suspiciously much for us */
+    return 0;
+
+  mem->memory = realloc(mem->memory, mem->size + realsize);
+  if(mem->memory == NULL)
+    /* out of memory! */
+    return 0;
+
+  memcpy(&(mem->memory[mem->size]), contents, realsize);
+  mem->size += realsize;
+
+  return realsize;
+}
+
+/* called from multi.c when this DOH transfer is complete */
+static int Curl_doh_done(struct Curl_easy *doh, CURLcode result)
+{
+  struct Curl_easy *data = doh->set.dohfor;
+  /* so one of the DOH request done for the 'data' transfer is now complete! */
+  data->req.doh.pending--;
+  infof(data, "a DOH request is completed, %d to go\n", data->req.doh.pending);
+  if(result)
+    infof(data, "DOH request %s\n", curl_easy_strerror(result));
+
+  if(!data->req.doh.pending) {
+    /* DOH completed */
+    curl_slist_free_all(data->req.doh.headers);
+    data->req.doh.headers = NULL;
+    Curl_expire(data, 0, EXPIRE_RUN_NOW);
+  }
+  return 0;
+}
+
+#define ERROR_CHECK_SETOPT(x,y) result = curl_easy_setopt(doh, x, y);   \
+  if(result) goto error
+
+static CURLcode dohprobe(struct Curl_easy *data,
+                         struct dnsprobe *p, DNStype dnstype,
+                         const char *host,
+                         const char *url, CURLM *multi,
+                         struct curl_slist *headers)
+{
+  struct Curl_easy *doh = NULL;
+  char *nurl = NULL;
+  CURLcode result = CURLE_OK;
+  timediff_t timeout_ms;
+  DOHcode d = doh_encode(host, dnstype, p->dohbuffer, sizeof(p->dohbuffer),
+                         &p->dohlen);
+  if(d) {
+    failf(data, "Failed to encode DOH packet [%d]\n", d);
+    return CURLE_OUT_OF_MEMORY;
+  }
+
+  p->dnstype = dnstype;
+  p->serverdoh.memory = NULL;
+  /* the memory will be grown as needed by realloc in the doh_write_cb
+     function */
+  p->serverdoh.size = 0;
+
+  /* Note: this is code for sending the DoH request with GET but there's still
+     no logic that actually enables this. We should either add that ability or
+     yank out the GET code. Discuss! */
+  if(data->set.doh_get) {
+    char *b64;
+    size_t b64len;
+    result = Curl_base64url_encode(data, (char *)p->dohbuffer, p->dohlen,
+                                   &b64, &b64len);
+    if(result)
+      goto error;
+    nurl = aprintf("%s?dns=%s", url, b64);
+    free(b64);
+    if(!nurl) {
+      result = CURLE_OUT_OF_MEMORY;
+      goto error;
+    }
+    url = nurl;
+  }
+
+  timeout_ms = Curl_timeleft(data, NULL, TRUE);
+
+  /* Curl_open() is the internal version of curl_easy_init() */
+  result = Curl_open(&doh);
+  if(!result) {
+    ERROR_CHECK_SETOPT(CURLOPT_URL, url);
+    ERROR_CHECK_SETOPT(CURLOPT_WRITEFUNCTION, doh_write_cb);
+    ERROR_CHECK_SETOPT(CURLOPT_WRITEDATA, (void *)&p->serverdoh);
+    if(!data->set.doh_get) {
+      ERROR_CHECK_SETOPT(CURLOPT_POSTFIELDS, &p->dohbuffer[0]);
+      ERROR_CHECK_SETOPT(CURLOPT_POSTFIELDSIZE, p->dohlen);
+    }
+    ERROR_CHECK_SETOPT(CURLOPT_HTTPHEADER, headers);
+    ERROR_CHECK_SETOPT(CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);
+#ifndef CURLDEBUG
+    /* enforce HTTPS if not debug */
+    ERROR_CHECK_SETOPT(CURLOPT_PROTOCOLS, CURLPROTO_HTTPS);
+#endif
+    ERROR_CHECK_SETOPT(CURLOPT_TIMEOUT_MS, (long)timeout_ms);
+    ERROR_CHECK_SETOPT(CURLOPT_VERBOSE, 1L);
+    doh->set.fmultidone = Curl_doh_done;
+    doh->set.dohfor = data; /* identify for which transfer this is done */
+    p->easy = doh;
+
+    /* add this transfer to the multi handle */
+    if(curl_multi_add_handle(multi, doh))
+      goto error;
+  }
+  else
+    goto error;
+  free(nurl);
+  return CURLE_OK;
+
+  error:
+  free(nurl);
+  Curl_close(doh);
+  return result;
+}
+
+/*
+ * Curl_doh() resolves a name using DOH. It resolves a name and returns a
+ * 'Curl_addrinfo *' with the address information.
+ */
+
+Curl_addrinfo *Curl_doh(struct connectdata *conn,
+                        const char *hostname,
+                        int port,
+                        int *waitp)
+{
+  struct Curl_easy *data = conn->data;
+  CURLcode result = CURLE_OK;
+  *waitp = TRUE; /* this never returns synchronously */
+  (void)conn;
+  (void)hostname;
+  (void)port;
+
+  /* start clean, consider allocating this struct on demand */
+  memset(&data->req.doh, 0, sizeof(struct dohdata));
+
+  data->req.doh.host = hostname;
+  data->req.doh.port = port;
+  data->req.doh.headers =
+    curl_slist_append(NULL,
+                      "Content-Type: application/dns-message");
+  if(!data->req.doh.headers)
+    goto error;
+
+  if(conn->ip_version != CURL_IPRESOLVE_V6) {
+    /* create IPv4 DOH request */
+    result = dohprobe(data, &data->req.doh.probe[0], DNS_TYPE_A,
+                      hostname, data->set.str[STRING_DOH],
+                      data->multi, data->req.doh.headers);
+    if(result)
+      goto error;
+    data->req.doh.pending++;
+  }
+
+  if(conn->ip_version != CURL_IPRESOLVE_V4) {
+    /* create IPv6 DOH request */
+    result = dohprobe(data, &data->req.doh.probe[1], DNS_TYPE_AAAA,
+                      hostname, data->set.str[STRING_DOH],
+                      data->multi, data->req.doh.headers);
+    if(result)
+      goto error;
+    data->req.doh.pending++;
+  }
+  return NULL;
+
+  error:
+  curl_slist_free_all(data->req.doh.headers);
+  data->req.doh.headers = NULL;
+  curl_easy_cleanup(data->req.doh.probe[0].easy);
+  data->req.doh.probe[0].easy = NULL;
+  curl_easy_cleanup(data->req.doh.probe[1].easy);
+  data->req.doh.probe[1].easy = NULL;
+  return NULL;
+}
+
+static DOHcode skipqname(unsigned char *doh, size_t dohlen,
+                         unsigned int *indexp)
+{
+  unsigned char length;
+  do {
+    if(dohlen < (*indexp + 1))
+      return DOH_DNS_OUT_OF_RANGE;
+    length = doh[*indexp];
+    if((length & 0xc0) == 0xc0) {
+      /* name pointer, advance over it and be done */
+      if(dohlen < (*indexp + 2))
+        return DOH_DNS_OUT_OF_RANGE;
+      *indexp += 2;
+      break;
+    }
+    if(length & 0xc0)
+      return DOH_DNS_BAD_LABEL;
+    if(dohlen < (*indexp + 1 + length))
+      return DOH_DNS_OUT_OF_RANGE;
+    *indexp += 1 + length;
+  } while(length);
+  return DOH_OK;
+}
+
+static unsigned short get16bit(unsigned char *doh, int index)
+{
+  return (unsigned short)((doh[index] << 8) | doh[index + 1]);
+}
+
+static unsigned int get32bit(unsigned char *doh, int index)
+{
+  return (doh[index] << 24) | (doh[index + 1] << 16) |
+    (doh[index + 2] << 8) | doh[index + 3];
+}
+
+struct addr6 {
+  unsigned char byte[16];
+};
+
+struct cnamestore {
+  size_t len;       /* length of cname */
+  char *alloc;      /* allocated pointer */
+  size_t allocsize; /* allocated size */
+};
+
+struct dohaddr {
+  int type;
+  union {
+    unsigned int v4;
+    struct addr6 v6;
+  } ip;
+};
+
+struct dohentry {
+  unsigned int ttl;
+  int numaddr;
+  struct dohaddr addr[MAX_ADDR];
+  int numcname;
+  struct cnamestore cname[MAX_ADDR];
+};
+
+static DOHcode store_a(unsigned char *doh, int index, struct dohentry *d)
+{
+  /* silently ignore addresses over the limit */
+  if(d->numaddr < MAX_ADDR) {
+    struct dohaddr *a = &d->addr[d->numaddr];
+    a->type = DNS_TYPE_A;
+    a->ip.v4 = ntohl(get32bit(doh, index));
+    d->numaddr++;
+  }
+  return DOH_OK;
+}
+
+static DOHcode store_aaaa(unsigned char *doh, int index, struct dohentry *d)
+{
+  /* silently ignore addresses over the limit */
+  if(d->numaddr < MAX_ADDR) {
+    struct dohaddr *a = &d->addr[d->numaddr];
+    struct addr6 *inet6p = &a->ip.v6;
+    a->type = DNS_TYPE_AAAA;
+    memcpy(inet6p, &doh[index], 16);
+    d->numaddr++;
+  }
+  return DOH_OK;
+}
+
+static DOHcode cnameappend(struct cnamestore *c,
+                           unsigned char *src,
+                           size_t len)
+{
+  if(!c->alloc) {
+    c->allocsize = len + 1;
+    c->alloc = malloc(c->allocsize);
+    if(!c->alloc)
+      return DOH_OUT_OF_MEM;
+  }
+  else if(c->allocsize < (c->allocsize + len + 1)) {
+    char *ptr;
+    c->allocsize += len + 1;
+    ptr = realloc(c->alloc, c->allocsize);
+    if(!ptr) {
+      free(c->alloc);
+      return DOH_OUT_OF_MEM;
+    }
+    c->alloc = ptr;
+  }
+  memcpy(&c->alloc[c->len], src, len);
+  c->len += len;
+  c->alloc[c->len] = 0; /* keep it zero terminated */
+  return DOH_OK;
+}
+
+static DOHcode store_cname(unsigned char *doh,
+                           size_t dohlen,
+                           unsigned int index,
+                           struct dohentry *d)
+{
+  struct cnamestore *c = &d->cname[d->numcname++];
+  unsigned int loop = 128; /* a valid DNS name can never loop this much */
+  unsigned char length;
+  do {
+    if(index >= dohlen)
+      return DOH_DNS_OUT_OF_RANGE;
+    length = doh[index];
+    if((length & 0xc0) == 0xc0) {
+      int newpos;
+      /* name pointer, get the new offset (14 bits) */
+      if((index + 1) >= dohlen)
+        return DOH_DNS_OUT_OF_RANGE;
+
+      /* move to the the new index */
+      newpos = (length & 0x3f) << 8 | doh[index + 1];
+      index = newpos;
+      continue;
+    }
+    else if(length & 0xc0)
+      return DOH_DNS_BAD_LABEL; /* bad input */
+    else
+      index++;
+
+    if(length) {
+      DOHcode rc;
+      if(c->len) {
+        rc = cnameappend(c, (unsigned char *)".", 1);
+        if(rc)
+          return rc;
+      }
+      if((index + length) > dohlen)
+        return DOH_DNS_BAD_LABEL;
+
+      rc = cnameappend(c, &doh[index], length);
+      if(rc)
+        return rc;
+      index += length;
+    }
+  } while(length && --loop);
+
+  if(!loop)
+    return DOH_DNS_LABEL_LOOP;
+  return DOH_OK;
+}
+
+static DOHcode rdata(unsigned char *doh,
+                     size_t dohlen,
+                     unsigned short rdlength,
+                     unsigned short type,
+                     int index,
+                     struct dohentry *d)
+{
+  /* RDATA
+     - A (TYPE 1):  4 bytes
+     - AAAA (TYPE 28): 16 bytes
+     - NS (TYPE 2): N bytes */
+  DOHcode rc;
+
+  switch(type) {
+  case DNS_TYPE_A:
+    if(rdlength != 4)
+      return DOH_DNS_RDATA_LEN;
+    rc = store_a(doh, index, d);
+    if(rc)
+      return rc;
+    break;
+  case DNS_TYPE_AAAA:
+    if(rdlength != 16)
+      return DOH_DNS_RDATA_LEN;
+    rc = store_aaaa(doh, index, d);
+    if(rc)
+      return rc;
+    break;
+  case DNS_TYPE_CNAME:
+    rc = store_cname(doh, dohlen, index, d);
+    if(rc)
+      return rc;
+    break;
+  default:
+    /* unsupported type, just skip it */
+    break;
+  }
+  return DOH_OK;
+}
+
+static DOHcode doh_decode(unsigned char *doh,
+                          size_t dohlen,
+                          DNStype dnstype,
+                          struct dohentry *d)
+{
+  unsigned char rcode;
+  unsigned short qdcount;
+  unsigned short ancount;
+  unsigned short type = 0;
+  unsigned short class;
+  unsigned short rdlength;
+  unsigned short nscount;
+  unsigned short arcount;
+  unsigned int index = 12;
+  DOHcode rc;
+
+  d->ttl = INT_MAX;
+
+  if(dohlen < 12)
+    return DOH_TOO_SMALL_BUFFER; /* too small */
+  if(doh[0] || doh[1])
+    return DOH_DNS_BAD_ID; /* bad ID */
+  rcode = doh[3] & 0x0f;
+  if(rcode)
+    return DOH_DNS_BAD_RCODE; /* bad rcode */
+
+  qdcount = get16bit(doh, 4);
+  while(qdcount) {
+    rc = skipqname(doh, dohlen, &index);
+    if(rc)
+      return rc; /* bad qname */
+    if(dohlen < (index + 4))
+      return DOH_DNS_OUT_OF_RANGE;
+    index += 4; /* skip question's type and class */
+    qdcount--;
+  }
+
+  ancount = get16bit(doh, 6);
+  while(ancount) {
+    unsigned int ttl;
+
+    rc = skipqname(doh, dohlen, &index);
+    if(rc)
+      return rc; /* bad qname */
+
+    if(dohlen < (index + 2))
+      return DOH_DNS_OUT_OF_RANGE;
+
+    type = get16bit(doh, index);
+    if((type != DNS_TYPE_CNAME) && (type != dnstype))
+      /* Not the same type as was asked for nor CNAME */
+      return DOH_DNS_UNEXPECTED_TYPE;
+    index += 2;
+
+    if(dohlen < (index + 2))
+      return DOH_DNS_OUT_OF_RANGE;
+    class = get16bit(doh, index);
+    if(DNS_CLASS_IN != class)
+      return DOH_DNS_UNEXPECTED_CLASS; /* unsupported */
+    index += 2;
+
+    if(dohlen < (index + 4))
+      return DOH_DNS_OUT_OF_RANGE;
+
+    ttl = get32bit(doh, index);
+    if(ttl < d->ttl)
+      d->ttl = ttl;
+    index += 4;
+
+    if(dohlen < (index + 2))
+      return DOH_DNS_OUT_OF_RANGE;
+
+    rdlength = get16bit(doh, index);
+    index += 2;
+    if(dohlen < (index + rdlength))
+      return DOH_DNS_OUT_OF_RANGE;
+
+    rc = rdata(doh, dohlen, rdlength, type, index, d);
+    if(rc)
+      return rc; /* bad rdata */
+    index += rdlength;
+    ancount--;
+  }
+
+  nscount = get16bit(doh, 8);
+  while(nscount) {
+    rc = skipqname(doh, dohlen, &index);
+    if(rc)
+      return rc; /* bad qname */
+
+    if(dohlen < (index + 8))
+      return DOH_DNS_OUT_OF_RANGE;
+
+    index += 2 + 2 + 4; /* type, class and ttl */
+
+    if(dohlen < (index + 2))
+      return DOH_DNS_OUT_OF_RANGE;
+
+    rdlength = get16bit(doh, index);
+    index += 2;
+    if(dohlen < (index + rdlength))
+      return DOH_DNS_OUT_OF_RANGE;
+    index += rdlength;
+    nscount--;
+  }
+
+  arcount = get16bit(doh, 10);
+  while(arcount) {
+    rc = skipqname(doh, dohlen, &index);
+    if(rc)
+      return rc; /* bad qname */
+
+    if(dohlen < (index + 8))
+      return DOH_DNS_OUT_OF_RANGE;
+
+    index += 2 + 2 + 4; /* type, class and ttl */
+
+    if(dohlen < (index + 2))
+      return DOH_DNS_OUT_OF_RANGE;
+
+    rdlength = get16bit(doh, index);
+    index += 2;
+    if(dohlen < (index + rdlength))
+      return DOH_DNS_OUT_OF_RANGE;
+    index += rdlength;
+    arcount--;
+  }
+
+  if(index != dohlen)
+    return DOH_DNS_MALFORMAT; /* something is wrong */
+
+  if((type != DNS_TYPE_NS) && !d->numcname && !d->numaddr)
+    /* nothing stored! */
+    return DOH_NO_CONTENT;
+
+  return DOH_OK; /* ok */
+}
+
+static void showdoh(struct Curl_easy *data,
+                    struct dohentry *d)
+{
+  int i;
+  infof(data, "TTL: %u seconds\n", d->ttl);
+  for(i = 0; i < d->numaddr; i++) {
+    struct dohaddr *a = &d->addr[i];
+    if(a->type == DNS_TYPE_A) {
+      infof(data, "DOH A: %d.%d.%d.%d\n",
+            a->ip.v4 & 0xff, (a->ip.v4>>8) & 0xff,
+            (a->ip.v4>>16) & 0xff, a->ip.v4 >>24);
+    }
+    else if(a->type == DNS_TYPE_AAAA) {
+      int j;
+      char buffer[128];
+      char *ptr;
+      size_t len;
+      snprintf(buffer, 128, "DOH AAAA: ");
+      ptr = &buffer[10];
+      len = 118;
+      for(j = 0; j < 16; j += 2) {
+        size_t l;
+        snprintf(ptr, len, "%s%02x%02x", j?":":"", d->addr[i].ip.v6.byte[j],
+                 d->addr[i].ip.v6.byte[j + 1]);
+        l = strlen(ptr);
+        len -= l;
+        ptr += l;
+      }
+      infof(data, "%s\n", buffer);
+    }
+  }
+  for(i = 0; i < d->numcname; i++) {
+    infof(data, "CNAME: %s\n", d->cname[i].alloc);
+  }
+}
+
+/*
+ * doh2ai()
+ *
+ * This function returns a pointer to the first element of a newly allocated
+ * Curl_addrinfo struct linked list filled with the data from a set of DOH
+ * lookups.  Curl_addrinfo is meant to work like the addrinfo struct does for
+ * a IPv6 stack, but usable also for IPv4, all hosts and environments.
+ *
+ * The memory allocated by this function *MUST* be free'd later on calling
+ * Curl_freeaddrinfo().  For each successful call to this function there
+ * must be an associated call later to Curl_freeaddrinfo().
+ */
+
+static Curl_addrinfo *
+doh2ai(const struct dohentry *de, const char *hostname, int port)
+{
+  Curl_addrinfo *ai;
+  Curl_addrinfo *prevai = NULL;
+  Curl_addrinfo *firstai = NULL;
+  struct sockaddr_in *addr;
+#ifdef ENABLE_IPV6
+  struct sockaddr_in6 *addr6;
+#endif
+  CURLcode result = CURLE_OK;
+  int i;
+
+  if(!de)
+    /* no input == no output! */
+    return NULL;
+
+  for(i = 0; i < de->numaddr; i++) {
+    size_t ss_size;
+    CURL_SA_FAMILY_T addrtype;
+    if(de->addr[i].type == DNS_TYPE_AAAA) {
+#ifndef ENABLE_IPV6
+      /* we can't handle IPv6 addresses */
+      continue;
+#else
+      ss_size = sizeof(struct sockaddr_in6);
+      addrtype = AF_INET6;
+#endif
+    }
+    else {
+      ss_size = sizeof(struct sockaddr_in);
+      addrtype = AF_INET;
+    }
+
+    ai = calloc(1, sizeof(Curl_addrinfo));
+    if(!ai) {
+      result = CURLE_OUT_OF_MEMORY;
+      break;
+    }
+    ai->ai_canonname = strdup(hostname);
+    if(!ai->ai_canonname) {
+      result = CURLE_OUT_OF_MEMORY;
+      free(ai);
+      break;
+    }
+    ai->ai_addr = calloc(1, ss_size);
+    if(!ai->ai_addr) {
+      result = CURLE_OUT_OF_MEMORY;
+      free(ai->ai_canonname);
+      free(ai);
+      break;
+    }
+
+    if(!firstai)
+      /* store the pointer we want to return from this function */
+      firstai = ai;
+
+    if(prevai)
+      /* make the previous entry point to this */
+      prevai->ai_next = ai;
+
+    ai->ai_family = addrtype;
+
+    /* we return all names as STREAM, so when using this address for TFTP
+       the type must be ignored and conn->socktype be used instead! */
+    ai->ai_socktype = SOCK_STREAM;
+
+    ai->ai_addrlen = (curl_socklen_t)ss_size;
+
+    /* leave the rest of the struct filled with zero */
+
+    switch(ai->ai_family) {
+    case AF_INET:
+      addr = (void *)ai->ai_addr; /* storage area for this info */
+
+      memcpy(&addr->sin_addr, &de->addr[i].ip.v4, sizeof(struct in_addr));
+      addr->sin_family = (CURL_SA_FAMILY_T)addrtype;
+      addr->sin_port = htons((unsigned short)port);
+      break;
+
+#ifdef ENABLE_IPV6
+    case AF_INET6:
+      addr6 = (void *)ai->ai_addr; /* storage area for this info */
+
+      memcpy(&addr6->sin6_addr, &de->addr[i].ip.v6, sizeof(struct in6_addr));
+      addr6->sin6_family = (CURL_SA_FAMILY_T)addrtype;
+      addr6->sin6_port = htons((unsigned short)port);
+      break;
+#endif
+    }
+
+    prevai = ai;
+  }
+
+  if(result) {
+    Curl_freeaddrinfo(firstai);
+    firstai = NULL;
+  }
+
+  return firstai;
+}
+
+static const char *type2name(DNStype dnstype)
+{
+  return (dnstype == DNS_TYPE_A)?"A":"AAAA";
+}
+
+static void de_cleanup(struct dohentry *d)
+{
+  int i = 0;
+  for(i = 0; i < d->numcname; i++) {
+    free(d->cname[i].alloc);
+  }
+}
+
+CURLcode Curl_doh_is_resolved(struct connectdata *conn,
+                              struct Curl_dns_entry **dnsp)
+{
+  struct Curl_easy *data = conn->data;
+  *dnsp = NULL; /* defaults to no response */
+
+  if(!data->req.doh.probe[0].easy && !data->req.doh.probe[1].easy) {
+    failf(data, "Could not DOH-resolve: %s", conn->async.hostname);
+    return conn->bits.proxy?CURLE_COULDNT_RESOLVE_PROXY:
+      CURLE_COULDNT_RESOLVE_HOST;
+  }
+  else if(!data->req.doh.pending) {
+    DOHcode rc;
+    DOHcode rc2;
+    struct dohentry de;
+    struct Curl_dns_entry *dns;
+    struct Curl_addrinfo *ai;
+    /* remove DOH handles from multi handle and close them */
+    curl_multi_remove_handle(data->multi, data->req.doh.probe[0].easy);
+    Curl_close(data->req.doh.probe[0].easy);
+    curl_multi_remove_handle(data->multi, data->req.doh.probe[1].easy);
+    Curl_close(data->req.doh.probe[1].easy);
+
+    /* parse the responses, create the struct and return it! */
+    memset(&de, 0, sizeof(de));
+    rc = doh_decode(data->req.doh.probe[0].serverdoh.memory,
+                    data->req.doh.probe[0].serverdoh.size,
+                    data->req.doh.probe[0].dnstype,
+                    &de);
+    free(data->req.doh.probe[0].serverdoh.memory);
+    if(rc) {
+      infof(data, "DOH: %s type %s for %s\n", doh_strerror(rc),
+            type2name(data->req.doh.probe[0].dnstype),
+            data->req.doh.host);
+    }
+    rc2 = doh_decode(data->req.doh.probe[1].serverdoh.memory,
+                     data->req.doh.probe[1].serverdoh.size,
+                     data->req.doh.probe[1].dnstype,
+                     &de);
+    free(data->req.doh.probe[1].serverdoh.memory);
+    if(rc2) {
+      infof(data, "DOG: %s type %s for %s\n", doh_strerror(rc2),
+            type2name(data->req.doh.probe[1].dnstype),
+            data->req.doh.host);
+    }
+    if(!rc || !rc2) {
+      infof(data, "DOH Host name: %s\n", data->req.doh.host);
+      showdoh(data, &de);
+
+      ai = doh2ai(&de, data->req.doh.host, data->req.doh.port);
+      if(!ai) {
+        de_cleanup(&de);
+        return CURLE_OUT_OF_MEMORY;
+      }
+
+      if(data->share)
+        Curl_share_lock(data, CURL_LOCK_DATA_DNS, CURL_LOCK_ACCESS_SINGLE);
+
+      /* we got a response, store it in the cache */
+      dns = Curl_cache_addr(data, ai, data->req.doh.host, data->req.doh.port);
+
+      if(data->share)
+        Curl_share_unlock(data, CURL_LOCK_DATA_DNS);
+
+      de_cleanup(&de);
+      if(!dns)
+        /* returned failure, bail out nicely */
+        Curl_freeaddrinfo(ai);
+      else {
+        conn->async.dns = dns;
+        *dnsp = dns;
+        return CURLE_OK;
+      }
+    }
+    de_cleanup(&de);
+
+    return CURLE_COULDNT_RESOLVE_HOST;
+  }
+
+  return CURLE_OK;
+}