httpuv
httpuv ships almost nothing, which is what you want from the web server under Shiny
Comparison · DevOps
callr vs Fiber
A side-by-side editorial comparison of callr and Fiber — release velocity, themes, recent moves, and the top alternatives to consider.
callr vs Fiber: at a glance
What is callr?
callr adds OpenTelemetry tracing, making R subprocess work observable across process boundaries
callr runs R code in fresh subprocesses and had been in maintenance for roughly two years — the 3.7.x releases are error-object polish, DLL handling, and Windows fixes. 3.8.0 breaks that pattern with a batch of substantive changes: pseudo-terminal support, carrier::crate() handling, configurable temp directories, honest non-zero exit statuses, and OpenTelemetry instrumentation.
What is Fiber?
Fiber v3 has sat in release candidate for months while v2 gets one-line patches
The feed carries two lines that barely touch. Fiber v2 receives narrow maintenance releases — a lock cleanup, an X-Real-IP backport, an HTML escaping fix, a CVE patch — most containing a single merged PR. The v3 line, last visible here at rc.3, is where the actual work is: native net/http and fasthttp handler support, Express-style request and response handlers, HostClient and LBClient in the client package.
callr vs Fiber: editorial side-by-side
callr
0.0DEVOPS
callr adds OpenTelemetry tracing, making R subprocess work observable across process boundaries
◆ Current state
callr runs R code in fresh subprocesses and had been in maintenance for roughly two years — the 3.7.x releases are error-object polish, DLL handling, and Windows fixes. 3.8.0 breaks that pattern with a batch of substantive changes: pseudo-terminal support, carrier::crate() handling, configurable temp directories, honest non-zero exit statuses, and OpenTelemetry instrumentation.
◆ Where it's heading
The package is being repositioned from a convenience wrapper into infrastructure that production R workloads can be operated against. Tracing spans that propagate a W3C traceparent into the child process, plus exit codes that finally reflect failure, are both about making callr legible to systems outside R. The pty and libpath changes point the same way — toward callr hosting long-lived, externally managed sessions.
◆ Prediction
Expect the OpenTelemetry surface to spread to sibling packages in the processx/r-lib process stack, and further work on subprocess failure semantics now that non-zero exits are the default.
Fiber
2.5DEVOPS
Fiber v3 has sat in release candidate for months while v2 gets one-line patches
◆ Current state
The feed carries two lines that barely touch. Fiber v2 receives narrow maintenance releases — a lock cleanup, an X-Real-IP backport, an HTML escaping fix, a CVE patch — most containing a single merged PR. The v3 line, last visible here at rc.3, is where the actual work is: native net/http and fasthttp handler support, Express-style request and response handlers, HostClient and LBClient in the client package.
◆ Where it's heading
v3 is the answer to Fiber's longest-standing objection, that building on fasthttp cuts a project off from the net/http middleware ecosystem. Making both handler styles native reframes Fiber as compatible rather than separate. But rc.3 dates to late 2025 and nothing newer has landed in this feed, while v2 patches keep arriving through August — a long release candidate stretch that leaves users choosing between a stable branch in pure maintenance and a v3 that has not been declared final.
◆ Prediction
The next meaningful entry is either a v3.0.0 final or a further RC; until one lands, expect the v2 line to continue receiving single-PR backports and security patches.
Alternatives to callr and Fiber
Other DevOps products tracked by Sparkpulse, ranked by recent ship velocity. Each card links to a full editorial trajectory and lets you pivot into a head-to-head comparison with either callr or Fiber.
promises
promises drops R6 for plain environments and wires async work into OpenTelemetry
withr
withr rebuilt defer() on base R's own on.exit(), and got much faster for it
htmltools
htmltools spends three releases walking back its own fill-layout opinions
xml2
xml2 relicensed to MIT, then moved its hot accessors from S3 into C
httr
httr's last releases are housekeeping - the package now points users at httr2
Recent activity from callr and Fiber
Latest ship moves from both products, interleaved chronologically. ⚡ = editorial spark.
- 23h agoFiberIdempotency middleware releases MemoryLock keys on unlock
- 1mo agoFiberX-Real-IP overwrite fix backported to v2
- 2mo agocallrOpenTelemetry tracing, pty support, and honest subprocess exit codes ⚡
- 3mo agoFiberCtx.Format now escapes HTML output
- 5mo agoFiberSecurity patch for GHSA-mrq8-rjmw-wpq3
- 6mo agoFiberMount improvements and limiter middleware fixes
- 8mo agoFiberv3 RC adds native net/http and Express-style handlers ⚡
- 2y agocallrEnv var to skip copying the client DLL
- 2y agocallrRunning-time fix and fully qualified subprocess calls
- 3y agocallrErrors carry subprocess stdout and stderr again
- 3y agocallrExperimental add_hook() for subprocess startup
- 4y agocallrUncompressed transport by default; revamped error objects
Frequently asked questions
What is the difference between callr and Fiber?
They serve adjacent needs but don't currently overlap on shipped themes. Fiber is currently shipping more aggressively (velocity 2.5 vs 0.0), with 0 editorial sparks in the last 30 days against 0. See the at-a-glance table above for a side-by-side breakdown of velocity, recent sparks, and editorial themes.
Is callr better than Fiber?
Sparkpulse doesn't pick a winner — we score release velocity, not feature parity. Fiber is currently shipping more aggressively (velocity 2.5 vs 0.0), with 0 editorial sparks in the last 30 days against 0. For your specific use case, the alternatives sections above list other DevOps products to evaluate alongside.
What are the best alternatives to callr?
Top callr alternatives in DevOps are ranked by recent ship velocity. Browse the "callr alternatives" section above for the current picks, or visit /alternatives/callr for the full list with editorial commentary on each.
What are the best alternatives to Fiber?
Top Fiber alternatives in DevOps are ranked by recent ship velocity. Browse the "Fiber alternatives" section above for the current picks, or visit /alternatives/fiber for the full list with editorial commentary on each.