Flow

The flow describes how the incoming request from the client is transformed into the outgoing response. The flow comprises actions, control structures and variables.

Each endpoint of your API can have its individual flow specified by x-flat-flow, see Routing.

Here we have a flow with if-elseif-else conditional statements and some echo actions evaluating the $request variable:

<flow>
  <if test="$request/query = 42">
    <echo>Yeah, that's it!</echo>
  </if>
  <elseif test="$request/query">
    <echo>Um, no!</echo>
  </elseif>
  <else>
    <echo>Do you know the answer?</echo>
  </else>
</flow>

Control Structures

break

break stops the flow processing for the current request. It may be used in sub flows or the init flow, too.

Response processing (such as validation and sending out the response) will continue, though.

A break statement should usually be executed conditionally, because otherwise none of the following statements will ever be executed.

<flow>
  <break/>
  <echo>will never be reached</echo>
</flow>

See also:

• echo
• dump
• return
• sub-flow

if-elseif-else

The if statement and the optional elseif and else statements allow for conditional execution of flow blocks.

<flow>
  <if test="…">…</if>

  <if test="…">…</if>
  <else>…</else>

  <if test="…">…</if>
  <elseif test="…">…</elseif>

  <if test="…">…</if>
  <elseif test="…">…</elseif>
  <elseif test="…">…</elseif>
  <else>…</else>
</flow>

Conditional expressions are defined in the test="…" attributes of the if and elseif statements. If such an expression evaluates to true, the flow block inside that if (or elseif) will be executed. All directly following elseif and else blocks will then be skipped.

If the result of that expression is false, the block will be skipped and the condition of the following elseif statement will be checked, if applicable.

The block associated with the first matching conditional expression will be executed – or if all expressions were evaluated to false, the else block will be executed.

if attribute

The if attribute allows for conditional execution of a single action:

<flow>
  …
  <error if="$upstream/my_request/status != 200">
  {
    …
  }
  </error>
  …
</flow>

return

return quits the current sub flow and returns to its parent flow. If return is used in the init flow the regular API path flow will still be executed. A return statement on the top-most flow behaves like break.