# Transcode lockfiles without solving

Use the lockfile fast path when an existing lockfile already contains every
requested platform and the output is another lockfile format.

The examples use a `pixi.lock` previously written through conda-presto by
conda-lockfiles' `pixi-lock-v6` exporter. Other lockfile versions require an
installed conda environment-specifier plugin that supports them.

## Transcode from the CLI

Pass one input lockfile, its covered platforms, and a lockfile exporter:

```bash
conda presto \
  --file pixi.lock \
  --platform linux-64 \
  --platform osx-arm64 \
  --format conda-lock-v1 \
  > conda-lock.yml
```

The CLI reuses the parsed package records and does not invoke the solver only
when all of these conditions hold:

- exactly one input file is provided
- that input is recognized as a lockfile
- every requested platform is present
- the output format is recognized as a lockfile
- no inline specs are added
- channels are not overridden

If those conditions do not hold, the normal CLI path may solve the combined
request instead.

## Transcode through the HTTP API

The `/transcode` endpoint is stricter than the CLI. It rejects a request that
would require a solve. Conda-presto's compatibility path builds and serializes
temporary package records inside the isolated parser process using only metadata
already present in the upload. It does not fetch package archives:

```bash
export CONDA_PRESTO_URL=http://127.0.0.1:8000

curl --fail --silent --show-error \
  --data-binary @pixi.lock \
  --header 'Content-Type: application/yaml' \
  "$CONDA_PRESTO_URL/transcode?filename=pixi.lock&platform=linux-64&platform=osx-arm64&format=conda-lock-v1" \
  --output conda-lock.yml
```

Use `filename` when the media type does not identify the lockfile parser.
The no-fetch path currently targets the `conda-lock-v1` and
`rattler-lock-v6` exporters supplied by conda-lockfiles, including their
aliases.

:::{note}
The temporary compatibility path rejects source data it cannot carry through
conda's environment model without changing package selection or solver
constraints. This can apply even when the source and target formats match. See
{ref}`http-transcode` for the exact rejection cases.
:::

## Diagnose a rejected transcode

Remove `--fail` temporarily to inspect an HTTP 400 response. The `reasons` list
identifies missing platforms, a non-lockfile input or output, or request fields
that would require a solve.

Available lockfile exporters are listed in
{doc}`../reference/output-formats`. For a normal environment-to-lockfile solve,
use {doc}`resolve-from-cli` or {doc}`call-http-api`.