# 3.5. CouchDB HTTP Server

## 3.5.1. HTTP Server Options

`[chttpd]`

Note

In CouchDB 2.x, the chttpd section refers to the standard, clustered port. All use of CouchDB, aside from a few specific maintenance tasks as described in this documentation, should be performed over this port.

> Defines the IP address by which the clustered port is available:

>     [chttpd]
>     bind_address = 127.0.0.1

> To let CouchDB listen any available IP address, use 0.0.0.0:

>     [chttpd]
>     bind_address = 0.0.0.0

> For IPv6 support you need to set ::1 if you want to let CouchDB listen correctly:

>     [chttpd]
>     bind_address = ::1

> or :: for any available:

>     [chttpd]
>     bind_address = ::

`port`

  Defines the port number to listen:

      [chttpd]
      port = 5984

  To let CouchDB use any free port, set this option to 0:

      [chttpd]
      port = 0

`prefer_minimal`

  If a request has the header “Prefer”: “return=minimal”, CouchDB will only send the headers that are listed for the prefer_minimal configuration.:

      [chttpd]
      prefer_minimal = Cache-Control, Content-Length, Content-Range, Content-Type, ETag, Server, Transfer-Encoding, Vary

  Warning

  Removing the Server header from the settings will mean that the CouchDB server header is replaced with the MochiWeb server header.

`authentication_handlers`

  List of authentication handlers used by CouchDB. You may extend them via third-party plugins or remove some of them if you won’t let users to use one of provided methods:

      [chttpd]
      authentication_handlers = {chttpd_auth, cookie_authentication_handler}, {chttpd_auth, default_authentication_handler}

  - `{chttpd_auth, cookie_authentication_handler}`: used for Cookie auth;
  - `{couch_httpd_auth, proxy_authentication_handler}`: used for Proxy auth;
  - `{chttpd_auth, default_authentication_handler}`: used for Basic auth;
  - `{couch_httpd_auth, null_authentication_handler}`: disables auth. Everlasting Admin Party!

`[httpd]`

Warning

In CouchDB 2.x, the httpd section mostly refers to the node-local port, on port 5986 by default. This port is used only for maintenance and administrative tasks. It should not be used for regular CouchDB access, and for security reasons, should always be bound to localhost (127.0.0.1) or a private LAN segment only.

`allow_jsonp`

  The `true` value of this option enables JSONP support (it’s `false` by default):

      [httpd]
      allow_jsonp = false

`bind_address`

  Defines the IP address by which the node-local port is available. The recommended setting is always:

      [httpd]
      bind_address = 127.0.0.1

  For IPv6 support you need to set ::1 if you want to let CouchDB listen correctly:

      [httpd]
      bind_address = ::1

`changes_timeout`

  Specifies default timeout value for Changes Feed in milliseconds (60000 by default):

      [httpd]
      changes_feed = 60000 ; 60 seconds

`config_whitelist`

  Sets the configuration modification whitelist. Only whitelisted values may be changed via the config API. To allow the admin to change this value over HTTP, remember to include `{httpd,config_whitelist}` itself. Excluding it from the list would require editing this file to update the whitelist:

      [httpd]
      config_whitelist = [{httpd,config_whitelist}, {log,level}, {etc,etc}]

`default_handler`

  Specifies default HTTP requests handler:

      [httpd]
      default_handler = {couch_httpd_db, handle_request}

`enable_cors`

  New in version 1.3.

  Controls CORS feature:

      [httpd]
      enable_cors = false

`port`

  Defines the port number to listen:

      [httpd]
      port = 5986

  To let CouchDB use any free port, set this option to `0`:

      [httpd]
      port = 0

`redirect_vhost_handler`

  This option customizes the default function that handles requests to `virtual hosts`:

      [httpd]
      redirect_vhost_handler = {Module, Fun}

  The specified function take 2 arguments: the MochiWeb request object and the target path.

`server_options`

  Server options for the MochiWeb component of CouchDB can be added to the configuration files:

      [httpd]
      server_options = [{backlog, 128}, {acceptor_pool_size, 16}]

`secure_rewrites`

  This option allow to isolate databases via subdomains:

      [httpd]
      secure_rewrites = true

`socket_options`

  The socket options for the listening socket in CouchDB can be specified as a list of tuples. For example:

      [httpd]
      socket_options = [{recbuf, 262144}, {sndbuf, 262144}, {nodelay, true}]

  The options supported are a subset of full options supported by the TCP/IP stack. A list of the supported options are provided in the Erlang inet documentation.

`vhost_global_handlers`

  List of global handlers that are available for `virtual hosts`:

      [httpd]
      vhost_global_handlers = _utils, _uuids, _session, _users

`x_forwarded_host`

  The x_forwarded_host header (`X-Forwarded-Host` by default) is used to forward the original value of the `Host` header field in case, for example, if a reverse proxy is rewriting the “Host” header field to some internal host name before forward the request to CouchDB:

      [httpd]
      x_forwarded_host = X-Forwarded-Host

  This header has higher priority above `Host` one, if only it exists in the request.

`x_forwarded_proto`

  x_forwarded_proto header (`X-Forwarder-Proto` by default) is used for identifying the originating protocol of an HTTP request, since a reverse proxy may communicate with CouchDB instance using HTTP even if the request to the reverse proxy is HTTPS:

      [httpd]
      x_forwarded_proto = X-Forwarded-Proto

`x_forwarded_ssl`

  The x_forwarded_ssl header (`X-Forwarded-Ssl` by default) tells CouchDB that it should use the https scheme instead of the http. Actually, it’s a synonym for `X-Forwarded-Proto: https` header, but used by some reverse proxies:

      [httpd]
      x_forwarded_ssl = X-Forwarded-Ssl

`enable_xframe_options`

  Controls Enables or disabled feature:

      [httpd]
      enable_xframe_options = false

`WWW-Authenticate`

  Set this option to trigger basic-auth pop-up on unauthorized requests:

      [httpd]
      WWW-Authenticate = Basic realm="Welcome to the Couch!"

`max_http_request_size`

  Changed in version 2.1.0.

  Limit the maximum size of the HTTP request body. This setting applies to all requests and it doesn’t discriminate between single vs. multi-document operations. So setting it to 1MB would block a PUT of a document larger than 1MB, but it might also block a _bulk_docs update of 1000 1KB documents, or a multipart/related update of a small document followed by two 512KB attachments. This setting is intended to be used as a protection against maliciously large HTTP requests rather than for limiting maximum document sizes.

      [httpd]
      max_http_request_size = 4294967296 ; 4 GB

  Warning

  Before version 2.1.0 `couchdb/max_document_size` was implemented effectively as `max_http_request_size`. That is, it checked HTTP request bodies instead of document sizes. After the upgrade, it is advisable to review the usage of these configuration settings.

## 3.5.2. Secure Socket Level Options

`[ssl]`

  CouchDB supports SSL natively. All your secure connection needs can now be served without needing to set up and maintain a separate proxy server that handles SSL.

  SSL setup can be tricky, but the configuration in CouchDB was designed to be as easy as possible. All you need is two files; a certificate and a private key. If you bought an official SSL certificate from a certificate authority, both should be in your possession already.

  If you just want to try this out and don’t want to pay anything upfront, you can create a self-signed certificate. Everything will work the same, but clients will get a warning about an insecure certificate.

  You will need the OpenSSL command line tool installed. It probably already is.

      shell> mkdir /etc/couchdb/cert
      shell> cd /etc/couchdb/cert
      shell> openssl genrsa > privkey.pem
      shell> openssl req -new -x509 -key privkey.pem -out couchdb.pem -days 1095
      shell> chmod 600 privkey.pem couchdb.pem
      shell> chown couchdb privkey.pem couchdb.pem

  Now, you need to edit CouchDB’s configuration, by editing your `local.ini` file. Here is what you need to do.

  At first, `enable the HTTPS daemon`:

      [daemons]
      httpsd = {chttpd, start_link, [https]}

  Next, under the `[ssl]` section set up the newly generated certificates:

      [ssl]
      cert_file = /etc/couchdb/cert/couchdb.pem
      key_file = /etc/couchdb/cert/privkey.pem

  For more information please read certificates HOWTO.

  Now start (or restart) CouchDB. You should be able to connect to it using HTTPS on port 6984:

      shell> curl https://127.0.0.1:6984/
      curl: (60) SSL certificate problem, verify that the CA cert is OK. Details:
      error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
      More details here: http://curl.haxx.se/docs/sslcerts.html

      curl performs SSL certificate verification by default, using a "bundle"
      of Certificate Authority (CA) public keys (CA certs). If the default
      bundle file isn't adequate, you can specify an alternate file
      using the --cacert option.
      If this HTTPS server uses a certificate signed by a CA represented in
      the bundle, the certificate verification probably failed due to a
      problem with the certificate (it might be expired, or the name might
      not match the domain name in the URL).
      If you'd like to turn off curl's verification of the certificate, use
      the -k (or --insecure) option.

  Oh no! What happened?! Remember, clients will notify their users that your certificate is self signed. `curl` is the client in this case and it notifies you. Luckily you trust yourself (don’t you?) and you can specify the `-k` option as the message reads:

      shell> curl -k https://127.0.0.1:6984/
      {"couchdb":"Welcome","version":"1.5.0"}

  All done.

  `cacert_file`

    The path to a file containing PEM encoded CA certificates. The CA certificates are used to build the server certificate chain, and for client authentication. Also the CAs are used in the list of acceptable client CAs passed to the client when a certificate is requested. May be omitted if there is no need to verify the client and if there are not any intermediate CAs for the server certificate:

        [ssl]
        cacert_file = /etc/ssl/certs/ca-certificates.crt

  `cert_file`

    Path to a file containing the user’s certificate:

        [ssl]
        cert_file = /etc/couchdb/cert/couchdb.pem

  `key_file`

    Path to file containing user’s private PEM encoded key:

        [ssl]
        key_file = /etc/couchdb/cert/privkey.pem

  `password`

    String containing the user’s password. Only used if the private key file is password protected:

        [ssl]
        password = somepassword

  `ssl_certificate_max_depth`

    Maximum peer certificate depth (must be set even if certificate validation is off):

        [ssl]
        ssl_certificate_max_depth = 1

  `verify_fun`

    The verification fun (optional) if not specified, the default verification fun will be used:

        [ssl]
        verify_fun = {Module, VerifyFun}

  `verify_ssl_certificates`

    Set to true to validate peer certificates:

        [ssl]
        verify_ssl_certificates = false

  `fail_if_no_peer_cert`

    Set to true to terminate the TLS/SSL handshake with a handshake_failure alert message if the client does not send a certificate. Only used if verify_ssl_certificates is true. If set to false it will only fail if the client sends an invalid certificate (an empty certificate is considered valid):

        [ssl]
        fail_if_no_peer_cert = false

  `secure_renegotiate`

    Set to true to reject renegotiation attempt that does not live up to RFC 5746:

        [ssl]
        secure_renegotiate = true

  `ciphers`

    Set to the cipher suites that should be supported which can be specified in erlang format “{ecdhe_ecdsa,aes_128_cbc,sha256}” or in OpenSSL format “ECDHE-ECDSA-AES128-SHA256”.

        [ssl]
        ciphers = ["ECDHE-ECDSA-AES128-SHA256", "ECDHE-ECDSA-AES128-SHA"]

  `tls_versions`

    Set to a list of permitted SSL/TLS protocol versions:

        [ssl]
        tls_versions = [tlsv1 | 'tlsv1.1' | 'tlsv1.2']

## 3.5.3. Cross-Origin Resource Sharing

`[cors]`

  New in version 1.3: added CORS support, see JIRA COUCHDB-431

  CORS, or “Cross-Origin Resource Sharing”, allows a resource such as a web page running JavaScript inside a browser, to make AJAX requests (XMLHttpRequests) to a different domain, without compromising the security of either party.

  A typical use case is to have a static website hosted on a CDN make requests to another resource, such as a hosted CouchDB instance. This avoids needing an intermediary proxy, using JSONP or similar workarounds to retrieve and host content.

  While CouchDB’s integrated HTTP server has support for document attachments makes this less of a constraint for pure CouchDB projects, there are many cases where separating the static content from the database access is desirable, and CORS makes this very straightforward.

  By supporting CORS functionality, a CouchDB instance can accept direct connections to protected databases and instances, without the browser functionality being blocked due to same-origin constraints. CORS is supported today on over 90% of recent browsers.

  CORS support is provided as experimental functionality in 1.3, and as such will need to be enabled specifically in CouchDB’s configuration. While all origins are forbidden from making requests by default, support is available for simple requests, preflight requests and per-vhost configuration.

  This section requires `httpd/enable_cors` option have `true` value:

      [httpd]
      enable_cors = true

  `credentials`

    By default, neither authentication headers nor cookies are included in requests and responses. To do so requires both setting `XmlHttpRequest.withCredentials = true` on the request object in the browser and enabling credentials support in CouchDB.

        [cors]
        credentials = true

    CouchDB will respond to a credentials-enabled CORS request with an additional header, `Access-Control-Allow-Credentials=true`.

  `origins`

    List of origins separated by a comma, `*` means accept all. You can’t set `origins = *` and `credentials = true` option at the same time:

        [cors]
        origins = *

    Access can be restricted by protocol, host and optionally by port. Origins must follow the scheme: http://example.com:80:

        [cors]
        origins = http://localhost, https://localhost, http://couch.mydev.name:8080

    Note that by default, no origins are accepted. You must define them explicitly.

  `headers`

    List of accepted headers separated by a comma:

        [cors]
        headers = X-Couch-Id, X-Couch-Rev

  `methods`

    List of accepted methods:

        [cors]
        methods = GET,POST

  See also

  Original JIRA implementation ticket

  Standards and References:

  - IETF RFCs relating to methods: RFC 2618, RFC 2817, RFC 5789
  - IETF RFC for Web Origins: RFC 6454
  - W3C CORS standard

  Mozilla Developer Network Resources:

  - Same origin policy for URIs
  - HTTP Access Control
  - Server-side Access Control
  - JavaScript same origin policy

  Client-side CORS support and usage:

  - CORS browser support matrix
  - COS tutorial
  - XHR with CORS

### 3.5.3.1. Per Virtual Host Configuration

To set the options for a `vhosts`, you will need to create a section with the vhost name prefixed by `cors:`. Example case for the vhost example.com:

    [cors:example.com]
    credentials = false
    ; List of origins separated by a comma
    origins = *
    ; List of accepted headers separated by a comma
    headers = X-CouchDB-Header
    ; List of accepted methods
    methods = HEAD, GET

## 3.5.4. Virtual Hosts

`[vhosts]`

  CouchDB can map requests to different locations based on the `Host` header, even if they arrive on the same inbound IP address.

  This allows different virtual hosts on the same machine to map to different databases or design documents, etc. The most common use case is to map a virtual host to a Rewrite Handler, to provide full control over the application’s URIs.

  To add a virtual host, add a CNAME pointer to the DNS for your domain name. For development and testing, it is sufficient to add an entry in the hosts file, typically /etc/hosts` on Unix-like operating systems:

      # CouchDB vhost definitions, refer to local.ini for further details
      127.0.0.1       couchdb.local

  Test that this is working:

      $ ping -n 2 couchdb.local
      PING couchdb.local (127.0.0.1) 56(84) bytes of data.
      64 bytes from localhost (127.0.0.1): icmp_req=1 ttl=64 time=0.025 ms
      64 bytes from localhost (127.0.0.1): icmp_req=2 ttl=64 time=0.051 ms

  Finally, add an entry to your configuration file in the `[vhosts]` section:

      [vhosts]
      couchdb.local:5984 = /example
      *.couchdb.local:5984 = /example

  If your CouchDB is listening on the the default HTTP port (80), or is sitting behind a proxy, then you don’t need to specify a port number in the vhost key.

  The first line will rewrite the request to display the content of the example database. This rule works only if the `Host` header is `couchdb.local` and won’t work for CNAMEs. The second rule, on the other hand, matches all CNAMEs to example db, so that both www.couchdb.local and db.couchdb.local will work.

### 3.5.4.1. Rewriting Hosts to a Path

Like in the _rewrite handler you can match some variable and use them to create the target path. Some examples:

    [vhosts]
    *.couchdb.local = /*
    :dbname. = /:dbname
    :ddocname.:dbname.example.com = /:dbname/_design/:ddocname/_rewrite

The first rule passes the wildcard as dbname. The second one does the same, but uses a variable name. And the third one allows you to use any URL with ddocname in any database with dbname.

You could also change the default function to handle request by changing the setting `httpd/redirect_vhost_handler`.

## 3.5.5. X-Frame-Options

X-Frame-Options is a response header that controls whether a http response can be embedded in a <frame>, <iframe> or <object>. This is a security feature to help against clickjacking.

> [x_frame_options] ; Settings same-origin will return X-Frame-Options: SAMEORIGIN. ; If same origin is set, it will ignore the hosts setting ; same_origin = true ; Settings hosts will ; return X-Frame-Options: ALLOW-FROM https://example.com/ ; List of hosts separated by a comma. * means accept all ; hosts =

If xframe_options is enabled it will return X-Frame-Options: DENY by default. If same_origin is enabled it will return X-Frame-Options: SAMEORIGIN. A X-FRAME-OPTIONS: ALLOW-FROM url will be returned when same_origin is false, and the HOST header matches one of the urls in the hosts config. Otherwise a X-Frame-Options: DENY will be returned.