HTTP(s) (im_http)

This module listens for HTTP or HTTPS connections on the address and port defined by the ListenAddr directive. It accepts HTTP requests that include content and use methods such as POST, PUT, or PATCH. However, the module does not distinguish between the different HTTP methods. When using compression, im_http accepts requests with the Content-Encoding header set to identity, deflate, and gzip.

The log event must be included in the request body as raw data and will be available in the $raw_event field. The request must include the Content-Length header indicating the size of the event, and the module will read the number of bytes specified by this header. The module does not close connections while receiving valid requests to operate in Keep-Alive mode. It responds with HTTP/1.1 200 OK to each valid request. This acknowledgment ensures reliable message delivery.

im_http contains a partial HTTP/1.1 implementation designed to work with the om_http module. It has received limited interoperability testing, and thus, using it with other third-party clients may not have the expected results.

To examine the supported platforms, see the list of installation packages.

Configuration

The im_http module accepts the following directives in addition to the common module directives.

HTTPS directives

The following directives configure secure data transfer via HTTPS.

HTTPSAllowExpired

Set this directive to TRUE to allow connections with remote hosts presenting an expired certificate. The default is FALSE; the module rejects connections with expired certificates. This directive only takes effect when HTTPSRequireCert is set to TRUE.

HTTPSAllowHostnameValidation

Set this directive to TRUE to require that the certificate FQDN matches the server hostname before allowing a connection. The default is FALSE; the module does not validate the remote server hostname.

HTTPSAllowUntrusted

Set this directive to TRUE to allow connections with remote hosts regardless of certificate verification results. The default is FALSE; the module only accepts connections with trusted certificates.

HTTPSCADir

Set this directive to the path of a directory containing Certificate Authority (CA) certificates. The module uses these certificates to verify the certificate presented by the remote host. Name the certificate files using the OpenSSL hashed format: the hash of the certificate followed by .0, .1, and so on. To find the hash of a certificate using OpenSSL:

$ openssl x509 -hash -noout -in ca.crt

For example, if the certificate hash is e2f14e4a, name the certificate file e2f14e4a.0. If there is another certificate with the same hash, name it e2f14e4a.1, and so on.

To trust a remote host’s self-signed certificate, include a copy of it in this directory.

If this directive isn’t specified, NXLog Agent falls back to the default operating system root certificate store. Unix-like operating systems commonly store root certificates in /etc/ssl/certs. Windows operating systems use the Windows Certificate Store, while macOS uses the Keychain Access Application as the default certificate store. See Certificate Authority (CA) certificates in the NXLog Platform User Guide for more information on using this directive.

In addition, Microsoft’s PKI repository contains root certificates for Microsoft services.

This directive is mutually exclusive with the HTTPSCAThumbprint, HTTPSCAPattern, and HTTPSSearchAllCertStores directives.

HTTPSCAFile

Set this directive to the path of the Certificate Authority (CA) certificate used to verify the certificate presented by the remote host. To trust a remote host’s self-signed certificate, specify the remote host’s certificate itself. For certificates signed by an intermediate CA, the specified certificate must contain the complete certificate chain (certificate bundle).

This directive is mutually exclusive with the HTTPSCAThumbprint, HTTPSCAPattern, and HTTPSSearchAllCertStores directives.

HTTPSCAPattern

Set this directive to a PCRE2-compliant regular expression to locate a suitable Certificate Authority (CA) certificate. This directive is supported on Windows and macOS.

On Windows, the certificate must be in the Windows Certificate Store. On macOS, the certificate must be in the system keychain.

NXLog Agent matches the pattern against a string built from the certificate’s fields in this order:

SUBJECT=<value>, CN=<value>; DN=CN=<value>, O=<value>, OU=<value>, L=<value>, ST=<value>, C=<value>; SAN=<value>

The pattern doesn’t need to match every field. Include only the fields you want to match, and use .*? to skip over the rest.

For example, the following pattern matches only the DN and SAN fields:

HTTPSCAPattern    'DN=CN=SERVER01\.example\.com.*?SAN=DNS:SERVER01\.example\.com'

This produces the following output in the NXLog Agent log file:

matching pattern [DN=CN=SERVER01\.example\.com;.*?SAN=DNS:SERVER01\.example\.com] to certificate [SUBJECT=US, ClientState, ClientCity, ClientCompany, ClientUnit, SERVER01.example.com, CN=SERVER01.example.com; DN=CN=SERVER01.example.com, O=ClientCompany, OU=ClientUnit, L=ClientCity, ST=ClientState, C=US; SAN=DNS:SERVER01.example.com; DNS:www.SERVER01.example.com; IP:127.0.0.3; ]

If the pattern matches multiple certificates, NXLog Agent uses the first match. If the certificate changes, restart NXLog Agent to apply the new certificate.

This directive is mutually exclusive with the HTTPSCAThumbprint, HTTPSCADir, HTTPSCAFile, and HTTPSSearchAllCertStores directives.

On macOS, keychain behavior and certificate requirements depend on your operating system version. Newer versions enforce stricter rules on certificate algorithms and key sizes. A certificate and private key may be imported into the keychain, yet remain unusable if they do not comply with the current macOS requirements. After importing, you may also need to give NXLog Agent permission to use the certificate in the keychain.

Check your operating system documentation to find out which certificates are trusted and valid. See also Apple’s certificate requirements for macOS.

HTTPSCAThumbprint

Set this directive to the thumbprint of the Certificate Authority (CA) certificate used to verify the certificate presented by the remote host. This directive is supported on Windows and macOS.

On Windows, copy the hexadecimal fingerprint string from Windows Certificate Manager (certmgr.msc). The certificate must be in a Windows certificate store accessible by NXLog Agent.

On macOS, obtain the hexadecimal fingerprint string from the Keychain Access application. The certificate must be accessible in the system keychain.

Whitespaces and colons are automatically removed.

This directive is mutually exclusive with the HTTPSCADir, HTTPSCAFile, HTTPSCAPattern, and HTTPSSearchAllCertStores directives.

Check your operating system documentation to find out which certificates are trusted and valid. See also Apple’s certificate requirements for macOS.

HTTPSCertFile

Set this directive to the path of the certificate file to present to the remote host during the HTTPS handshake.

HTTPSCertKeyFile

Set this directive to the path of the private key file corresponding to the certificate specified by HTTPSCertFile.

HTTPSCertPattern

Set this directive to a PCRE2-compliant pattern to identify the certificate and its corresponding private key. This directive is supported on Windows and macOS.

NXLog Agent matches the pattern against a string built from the certificate’s fields in this order:

SUBJECT=<value>, CN=<value>; DN=CN=<value>, O=<value>, OU=<value>, L=<value>, ST=<value>, C=<value>; SAN=<value>

The pattern doesn’t need to match every field. Include only the fields you want to match, and use .*? to skip over the rest.

On Windows, import the certificate in PFX format into the Local Computer\Personal certificate store.

On macOS, ensure the certificate and its private key are present in the System Keychain (/Library/Keychains/System.keychain).

During configuration, NXLog Agent resolves this directive into the corresponding HTTPSCertThumbprint value. If the pattern matches multiple certificates, NXLog Agent uses the first match. This directive is not dynamic; restart NXLog Agent to apply a changed certificate.

We recommend keeping the certificate storage referenced by this directive well-maintained for optimal performance.

This directive is mutually exclusive with the HTTPSCertThumbprint, HTTPSCertFile and HTTPSCertKeyFile directives.

Configuration examples:

HTTPSCertPattern    $hostname + 'Cert'

HTTPSCertPattern    DN=CN=Client\.example\.com;.*?SAN=DNS:Client\.example\.com

This produces the following output in the NXLog Agent log file:

matching pattern [DN=CN=Client\.example\.com;.*?SAN=DNS:Client\.example\.com] to certificate [SUBJECT=US, ClientState, ClientCity, ClientCompany, ClientUnit, Client.example.com, CN=Client.example.com; DN=CN=Client.example.com, O=ClientCompany, OU=ClientUnit, L=ClientCity, ST=ClientState, C=US; SAN=DNS:Client.example.com; DNS:www.Client.example.com; IP:127.0.0.3; ]

Check your operating system documentation to find out which certificates are trusted and valid. See also Apple’s certificate requirements for macOS.

HTTPSCertThumbprint

Set this directive to the thumbprint of the certificate to present to the remote host during the HTTPS handshake. Whitespaces and colons are automatically removed. This directive is supported on Windows and macOS.

On Windows, copy the hexadecimal fingerprint string from Windows Certificate Manager (certmgr.msc). Import the certificate to the Local Computer\Personal certificate store in PFX format. To create a PFX file from the certificate and private key using OpenSSL:

$ openssl pkcs12 -export -out server.pfx -inkey server.key -in server.pem

When the global directive UseCNGCertificates is set to FALSE, the private key must be exportable.

If you generate the certificate request using Windows Certificate Manager, enable the Make private key exportable option from the certificate properties.
If you import the certificate with the Windows Certificate Import Wizard, make sure that the Mark this key as exportable option is enabled.
If you migrate the certificate and associated private key from one Windows machine to another, select Yes, export the private key when exporting from the source machine.

When UseCNGCertificates is set to TRUE, the private key does not need to be exportable. For example, private keys stored on a TPM are always non-exportable.

On macOS, obtain the hexadecimal fingerprint string from the Keychain Access application. The certificate and its associated private key must be present in the System Keychain (/Library/Keychains/System.keychain).

For example:

HTTPSCertThumbprint    7c2cc5a5fb59d4f46082a510e74df17da95e2152

Check your operating system documentation to find out which certificates are trusted and valid. See also Apple’s certificate requirements for macOS.

HTTPSCRLDir

Set this directive to the path of a directory containing certificate revocation list (CRL) files. The module uses these files to reject connections from hosts presenting a revoked certificate. Name the files using the OpenSSL hashed format: the hash of the issuer followed by .r0, .r1, and so on. To find the hash of the issuer of a CRL file using OpenSSL:

$ openssl crl -hash -noout -in crl.pem

For example, if the hash is e2f14e4a, name the file e2f14e4a.r0. If there is another file with the same hash, name it e2f14e4a.r1, and so on.

HTTPSCRLFile

Set this directive to the path of the certificate revocation list (CRL) file used to reject connections from hosts presenting a revoked certificate. To generate a CRL file using OpenSSL:

$ openssl ca -gencrl -out crl.pem

HTTPSDHFile

Set this directive to the path of a file containing Diffie-Hellman parameters for key exchange. Generate the parameters using dhparam(1ssl). If this directive is not set, the module uses default parameters. See the OpenSSL Wiki for further details.

HTTPSKeyPass

Set this directive to the passphrase of the private key specified by HTTPSCertKeyFile. This directive applies only to encrypted private keys.

To generate a private key with Triple DES encryption using OpenSSL:

$ openssl genrsa -des3 -out server.key 2048

HTTPSLoadCertificateChains

Set this directive to TRUE to load the full certificate chain from the PEM file referenced by HTTPSCertFile, which may contain a single certificate or the complete chain. The default is FALSE; the module loads certificates from the operating system certificate store instead.

This directive is only supported on Windows.

HTTPSRequireCert

Set this directive to TRUE to require the remote host to present a certificate during the HTTPS handshake. The module refuses the connection if no certificate is presented. The default is TRUE.

HTTPSSearchAllCertStores

Set this directive to TRUE to load all available Windows certificates into NXLog Agent for use during remote certificate verification. Any required certificates must be in a Windows certificate store accessible by NXLog Agent. This directive is only supported on Windows and is mutually exclusive with the HTTPSCAThumbprint, HTTPSCAPattern, HTTPSCADir, and HTTPSCAFile directives.

HTTPSSSLCipher

Set this directive to override the permitted cipher list for TLSv1.2 and below. Use the format described in the ciphers(1ssl) man page. For example, specify RSA:!COMPLEMENTOFALL to include all ciphers with RSA authentication but exclude ciphers without encryption.

If RSA or DSA ciphers with Diffie-Hellman key exchange are used, set HTTPSDHFile to specify custom Diffie-Hellman parameters.

HTTPSSSLCiphersuites

Set this directive to override the permitted cipher list for TLSv1.3. Use the same format as HTTPSSSLCipher. Refer to the OpenSSL documentation for a list of valid TLS v1.3 cipher suites. The default is:

TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256

HTTPSSSLCompression

Set this directive to TRUE to compress data using zlib when sending over the network. The default is FALSE; the module sends data without compression.

Some Linux distributions, including Debian, provide an OpenSSL library without zlib support. The module emits a warning on startup if compression support is missing. The generic deb/rpm packages are bundled with a zlib-enabled libssl library.

HTTPSSSLProtocol

Set this directive to restrict the TLS/SSL protocols the module accepts. Specify a comma-separated list of the following values: SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2, and TLSv1.3. The default is TLSv1.2 and TLSv1.3. The OpenSSL library shipped by some Linux distributions does not support SSLv2 and SSLv3; these protocols will not work even if specified here.

HTTPSTLSCertLog

Set this directive to TRUE to log the remote host’s certificate details during the HTTPS handshake. When available, the module logs the Subject, Issuer, NotBefore, and NotAfter fields to the NXLog Agent log file. The default is FALSE.

This directive depends on the values of the HTTPSAllowUntrusted and HTTPSRequireCert directives:

HTTPSAllowUntrusted HTTPSRequireCert Outcome

FALSE

Output depends on HTTPSTLSCertLog value

FALSE

TRUE

Output depends on HTTPSTLSCertLog value

TRUE

FALSE

No output regardless of HTTPSTLSCertLog value

TRUE

Output depends on HTTPSTLSCertLog value

Sigalgs

Set this directive to the signature algorithm parameter to pass to the Windows SSL library. Accepted values depend on the available encryption providers. This directive is only supported on Windows.

SNI

Set this directive to the hostname to use for Server Name Indication (SNI) in HTTPS mode.

UseCNGCertificates

Set this directive to TRUE to use the Windows Cryptography API: Next Generation (CNG) to access the private keys of certificates identified by a thumbprint. This directive is only supported on Windows.

Optional directives

ListenAddr

Set this directive to the IP address or DNS hostname on which the module accepts connections. The default is localhost, which restricts access to the local machine and prevents connections from remote hosts.

Append the port number to the address using a colon separator (host:port). The default port is 80. For IPv6 addresses, enclose the address in square brackets ([addr]:port). Use 0.0.0.0:80 for IPv4 or [::]:80 for IPv6 to accept connections on all interfaces. NXLog Agent requires additional privileges to bind to ports below 1024 on Linux. See Granting additional Linux capabilities for more information.

You can specify this directive multiple times to accept connections on multiple addresses or ports within a single module instance. Set IPv4 and IPv6 addresses as separate entries. If you use a DNS name, keep the number of addresses or CNAMEs below 16 to avoid errors caused by DNS response size limits.

AllowIP

Set this directive to restrict incoming connections to specific IP addresses or networks. You can specify this directive multiple times to allow multiple IPs or networks. AllowIP has no effect unless ListenAddr is configured.

If AllowIP is not set, the module falls back to BlockIP to deny specific connections. If neither AllowIP nor BlockIP is set, the module does not restrict incoming connections.

The following IP address formats may be used:

0.0.0.0 (IPv4 address)
0.0.0.0/32 (IPv4 network with subnet bits)
0.0.0.0/0.0.0.0 (IPv4 network with subnet address)
aa::1 (IPv6 address)
aa::12/64 (IPv6 network with subnet bits)

BlockIP

Set this directive to deny incoming connections from specific IP addresses or networks. You can specify this directive multiple times to deny multiple IPs or networks. BlockIP has no effect unless ListenAddr is configured.

If BlockIP is not set, the module falls back to AllowIP to restrict incoming connections. If neither BlockIP nor AllowIP is set, the module does not restrict incoming connections.

The following IP address formats may be used:

0.0.0.0 (IPv4 address)
0.0.0.0/32 (IPv4 network with subnet bits)
0.0.0.0/0.0.0.0 (IPv4 network with subnet address)
aa::1 (IPv6 address)
aa::12/64 (IPv6 network with subnet bits)

MaxConnections

Set this directive to limit the number of concurrent active connections for a listening TCP socket. The default is 4294967295 (unlimited). When the limit is reached, the module rejects new connections and logs an error:

Number of allowed active connections(10) reached: 10. Refusing connection from 127.0.0.1

ConnectionIdleTimeout

Set this directive to close TCP connections that have been idle for longer than the specified number of seconds. The minimum value is 15 seconds. If this directive is not set, the module keeps idle TCP connections open indefinitely.

ExclusiveAddrUse

Set this directive to TRUE to prevent other processes or module instances from binding to the same port.

The default is FALSE; multiple module instances can bind to the same port.

This directive is only supported on Windows.

ReuseAddr

Set this directive to TRUE to allow the module instance to bind to a port that is already in use.

The default is TRUE; multiple module instances can listen on the same port and process data simultaneously.

ReusePort

Set this directive to TRUE to allow multiple module instances to listen on the same port. Each instance runs in a separate thread, allowing NXLog Agent to process incoming logs simultaneously.

The default is FALSE; multiple module instances cannot bind to the same port.

This directive is not supported on Windows.

Functions

The following functions are exported by im_http.

type: string get_abs_path(): Returns the absolute path of the URL.
type: string get_param(type: string name): Returns the value of the specific URL parameter.
type: string get_rel_path(): Returns the relative path of the URL.
type: string get_url(): Returns the full URL.
type: hash parse_header(): Returns the HTTP headers for the current record (last parsed http request) as a hash value.
type: string parse_header(type: string key): From the current record, this returns the HTTP header value of the key.

Procedures

The following procedures are exported by im_http.

parse_url_params();: Generates fields from URL query parameters.

Fields

The following fields are created by im_http.

$raw_event (type: string): The content received in the POST request.
$MessageSourceAddress (type: ipaddr): The IP address of the remote host.

Examples

Example 1. Receiving logs over HTTPS

This configuration listens for HTTPS connections from localhost. Received log messages are written to a file.

nxlog.conf

<Input http>
    Module              im_http
    ListenAddr          0.0.0.0:8888
    HTTPSCertFile       %CERTDIR%/server-cert.pem
    HTTPSCertKeyFile    %CERTDIR%/server-key.pem
    HTTPSCAFile         %CERTDIR%/ca.pem
    HTTPSRequireCert    TRUE
    HTTPSAllowUntrusted FALSE
</Input>

Example 2. Receiving logs over HTTPS using certificate thumbprints

This configuration uses the HTTPSCAThumbprint and HTTPSCertThumbprint directives for the verification of the Certificate Authority and the SSL handshake respectively.

nxlog.conf

<Input in_https>
    Module                 im_http
    ListenAddr             0.0.0.0:443
    HTTPSCAThumbprint      c2c902f736d39d37fd65c458afe0180ea799e443
    HTTPSCertThumbprint    7c2cc5a5fb59d4f46082a510e74df17da95e2152
    HTTPSSSLProtocol       TLSv1.2
</Input>

Example 3. Sending data to im_http over HTTPS

This script uses the curl utility to send data to an im_http instance. The log data is passed as an argument when executing the script.

The URL value needs to be replaced with a valid hostname according to the value specified by the ListenAddr directive.

The PORT value needs to be replaced with the actual port that im_http has been configured to listen on.

The USESSL value needs to be updated with the path to the client certificate, client certificate key, and certification authority files respectively. In this example, the files are located in a folder named keys located in the same path as the script.

im-http-curl-request.sh

URL=https://<hostname>
PORT=<port>
USESSL="--cert keys/client-cert.pem --key keys/client-key.pem --cacert keys/ca.pem"

BYTELEN=`printf "%s" "$1" | wc -c`

curl -v $USESSL -H "Content-Type:plain/text" -H "Content-Length:${BYTELEN}" -d "$1" $URL:$PORT

The script is executed by running the following command and passing the log data to it as an argument:

# path/to/im-http-curl-request.sh "My log line"

This bash script and other examples can be found in the NXLog public repository on GitLab.

Example 4. Parsing values from incoming HTTP headers

This configuration waits for HTTP packets and parses the incoming headers, then logs the requested information. It extracts the header values, such as the User-Agent and the Content-Length, first by requesting the specific field directly, then by parsing the entire header and extracting the value from the hash. Both calls use compound values, but they can be used with simple values, depending on the scope of the implementation.

nxlog.conf

<Input ihttp>
Module          im_http
ListenAddr      0.0.0.0:6060
<Exec>
    $$agent = parse_header("User-Agent");
    log_info("User Agent:" + $$agent);

    # retrieving a hash with the entire header
    $$entire_header = parse_header();
    log_info("Data segment size in Bytes:" + $$entire_header('Content-Length'));
    log_info("Entire header parsed:" + $$entire_header);
</Exec>
</Input>