# Inputs and Outputs
For items to be reusable, its inputs and outputs are API.
```dot process
digraph {
graph [
margin = 0.0
penwidth = 0
nodesep = 0.0
ranksep = 0.02
bgcolor = "transparent"
fontname = "helvetica"
fontcolor = "#7f7f7f"
rankdir = LR
]
node [
fontcolor = "#111111"
fontname = "monospace"
fontsize = 12
shape = "circle"
style = "filled"
width = 0.3
height = 0.3
margin = 0.04
color = "#9999aa"
fillcolor = "#ddddf5"
]
edge [
arrowsize = 0.7
color = "#7f7f7f"
fontcolor = "#7f7f7f"
]
subgraph cluster_a {
a [label = <<b>a</b>>]
a_text [shape="plain" style="" fontcolor="#7f7f7f" label = <<table border="0" cellborder="0" cellpadding="0"><tr>
<td><font point-size="15">📥</font></td>
<td balign="left">file<br/>download</td>
</tr></table>>]
subgraph cluster_a_params {
a_params_src [
label = "src"
margin = 0.0
fontsize = 8
width = 0.78
height = 0.19
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffaaff"
color = "#773377"
]
a_params_dest [
label = "dest"
margin = 0.0
fontsize = 8
width = 0.78
height = 0.19
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffaaff"
color = "#773377"
]
a_state [
margin = 0.0
fontsize = 8
shape = "none"
style = "filled,rounded"
color = "#667722"
label = <<table
style="rounded"
border="1"
cellborder="0"
cellpadding="1"
cellspacing="0"
bgcolor="#ffffaa"
>
<tr><td colspan="2"><b> FileDownload <br/>State</b></td></tr>
<tr>
<td align="left" balign="left"><b>path:</b></td>
<td align="left" balign="left">PathBuf</td>
</tr>
<tr>
<td align="left" balign="left"><b>md5:</b></td>
<td align="left" balign="left">Md5Sum</td>
</tr>
<tr><td cellpadding="1"></td></tr>
</table>>
]
}
a_params_src -> a_state [style = invis]
a_params_dest -> a_state [style = invis]
a -> a_state [style = invis]
}
subgraph cluster_b {
b [label = <<b>b</b>>]
b_text [shape="plain" style="" fontcolor="#7f7f7f" label = <<table border="0" cellborder="0" cellpadding="0"><tr>
<td><font point-size="15">🪣</font></td>
<td balign="left">s3<br/>bucket</td>
</tr></table>>]
subgraph cluster_b_params {
b_params_name [
label = "name"
margin = 0.0
fontsize = 8
width = 0.78
height = 0.19
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffaaff"
color = "#773377"
]
b_state [
margin = 0.0
fontsize = 8
shape = "none"
style = "filled,rounded"
color = "#667722"
label = <<table
style="rounded"
border="1"
cellborder="0"
cellpadding="1"
cellspacing="0"
bgcolor="#ffffaa"
>
<tr><td colspan="2"><b>S3Bucket<br/>State</b></td></tr>
<tr>
<td align="left" balign="left"><b>name:</b></td>
<td align="left" balign="left">String </td>
</tr>
<tr><td cellpadding="1"></td></tr>
</table>>
]
}
b_params_name -> b_state [style = invis]
b -> b_state [style = invis]
}
subgraph cluster_c {
c [label = <<b>c</b>>]
c_text [shape="plain" style="" fontcolor="#7f7f7f" label = <<table border="0" cellborder="0" cellpadding="0"><tr>
<td><font point-size="15">📤</font></td>
<td balign="left">s3<br/>object</td>
</tr></table>>]
subgraph cluster_c_params {
c_params_file_path [
label = "file_path"
margin = 0.0
fontsize = 8
width = 0.78
height = 0.19
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffaaff"
color = "#773377"
]
c_params_bucket_name [
label = "bucket_name"
margin = 0.0
fontsize = 8
width = 0.78
height = 0.19
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffaaff"
color = "#773377"
]
c_params_object_key [
label = "object_key"
margin = 0.0
fontsize = 8
width = 0.78
height = 0.19
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffaaff"
color = "#773377"
]
c_state [
margin = 0.0
fontsize = 8
shape = "none"
style = "filled,rounded"
color = "#667722"
label = <<table
style="rounded"
border="1"
cellborder="0"
cellpadding="1"
cellspacing="0"
bgcolor="#ffffaa"
>
<tr><td colspan="2"><b> S3Object <br/>State</b></td></tr>
<tr>
<td align="left" balign="left"></td>
<td align="left" balign="left">..</td>
</tr>
<tr><td cellpadding="1"></td></tr>
</table>>
]
}
c_params_file_path -> c_state [style = invis]
c_params_bucket_name -> c_state [style = invis]
c_params_object_key -> c_state [style = invis]
c -> c_state [style = invis]
}
a -> b [minlen = 9]
b -> c [minlen = 9]
}
```
### Item API
```rust ,ignore
impl<Id> Item for FileDownloadItem<Id>
{
type Params<'exec> = FileDownloadParams<Id>;
type State = FileDownloadState;
// ..
}
```
<div class="column_half">
Input:
```rust ,ignore
pub struct FileDownloadParams<Id> {
src: Url,
dest: PathBuf,
marker: PhantomData<Id>,
}
```
</div><div class="column_half">
Output:
```rust ,ignore
pub enum FileDownloadState {
None,
Some {
path: PathBuf,
md5: Md5Sum,
},
}
```
</div>
