How to Capture HTTP Streams Using 'httpflow' (with examples)

The ‘httpflow’ command-line utility is a powerful tool for capturing and analyzing HTTP streams directly from network interfaces. Whether you’re a network administrator troubleshooting issues, a security professional analyzing traffic for anomalies, or a developer testing API interactions, ‘httpflow’ provides a versatile set of features for your needs. By offering options to filter and capture data both in real time and from saved files, ‘httpflow’ makes HTTP traffic analysis accessible and flexible.

Use case 1: Capture traffic on all interfaces

Code:

httpflow -i any

Motivation:
Capturing traffic on all network interfaces is essential when you have multiple interfaces on your system and you want to monitor all outgoing and incoming HTTP requests. This is particularly useful in server environments or machines with multiple network connections (e.g., a combination of Ethernet, Wi-Fi, and VPN interfaces).

Explanation:

• -i any: This option specifies that ‘httpflow’ should capture packets from all available network interfaces on the machine. By default, capture tools operate on a single interface unless specified otherwise, but using ‘any’ ensures no HTTP traffic is missed during the capture session.

Example Output:
Using this command, you might see an output capturing HTTP requests and responses across all interfaces, displayed in real time. The output includes details like the source and destination IP addresses, ports, and HTTP method and status codes for each transaction.

Use case 2: Use a bpf-style capture to filter the results

Code:

httpflow host httpbin.org or host baidu.com

Motivation:
Filtering HTTP traffic by host ensures you only capture data relevant to specific domains or IP addresses, which is crucial in narrowing your focus. In scenarios where you’re only interested in traffic to and from specific sites (such as when testing API endpoints), bpf-style filters are incredibly useful for efficient monitoring.

Explanation:

• host httpbin.org or host baidu.com: This filter expression uses Berkeley Packet Filter (BPF) syntax to specify that only traffic directed to or from the hosts httpbin.org or baidu.com should be included in the capture. BPF filters are powerful and widely supported across various packet capture utilities, allowing for expressive and efficient traffic filtering.

Example Output:
The result of applying this filter would show HTTP requests and responses solely related to interactions with httpbin.org and baidu.com, omitting all other traffic for clearer analysis.

Use case 3: Use a regular expression to filter requests by URLs

Code:

httpflow -u 'regular_expression'

Motivation:
In environments where you need to pinpoint traffic to specific URL patterns, using regular expressions provides flexibility and precision. For instance, this technique is useful for filtering requests based on parameters or certain endpoints, allowing for an in-depth focus on particular HTTP transactions.

Explanation:

• -u 'regular_expression': The ‘-u’ flag instructs ‘httpflow’ to apply a regular expression to filter captured URLs. Regular expressions enable the user to define specific patterns for the URLs of interest, which can include wildcards, character classes, and other regex features to match complex URL patterns.

Example Output:
Once executed, this command might display HTTP exchanges that match a particular URL pattern set by the regular expression, helping isolate the traffic pertinent to the specified criteria.

Use case 4: Read packets from PCAP format binary file

Code:

httpflow -r out.cap

Motivation:
Reading packets from a pre-captured PCAP file allows offline analysis of network traffic. This use case is particularly valuable for post-event traffic analysis in forensic investigations, where network logs are examined to ascertain patterns, breaches, or failures after they have occurred.

Explanation:

• -r out.cap: The ‘-r’ option signals ‘httpflow’ to read input from a pre-existing PCAP file named out.cap. This mode bypasses live capture and instead processes stored packet data, which is beneficial for retrospective analysis sessions.

Example Output:
Executing this command processes the content of the file out.cap, displaying captured HTTP traffic as if monitoring in real time, thus recreating an analysis environment from static data.

Use case 5: Write the output to a directory

Code:

httpflow -w path/to/directory

Motivation:
Saving captured HTTP traffic into a directory structure is crucial for organized storage and later retrieval, especially when coordinating multiple analysis sessions or preserving logs for audit trails. This helps in building an archive for compliance or long-term data trends.

Explanation:

• -w path/to/directory: This option directs ‘httpflow’ to write its output into the specified directory. This directs all outputs from the capture session into a structured file system path, ensuring the organized storage of data for subsequent access and review.

Example Output:
When directing output to a directory, a variety of files, each containing captured HTTP data, will be systematically written to the specified path. These files can then be back-traced and opened individually for detailed perusal.

Conclusion:

The ‘httpflow’ command-line utility offers a rich feature set for capturing and inspecting HTTP streams over networks, making it a valuable tool for anyone needing a robust solution for traffic analysis. From real-time capture to precise filtering and offline analysis, ‘httpflow’ makes understanding and managing network traffic both flexible and comprehensive. Whether ensuring security, debugging issues, or monitoring API usage, ‘httpflow’ equips users with the needed functionalities wrapped in a simple command-line interface.